The ''You`re Banned'' Game

I ban Michael 'cos, Tau? They can outshoot Chaos easily but they won't catch up to them and can't really take it back either. Plus they're DLC, which I don't have yet.
The Eldar is fast like them, but I wouldn't call charging blindly into Lightning Strike or boarding pods range enlightened. Chaos is a rather good match-up against them since Eldar ships are faster, can avoid lance fire and their pulsars hit like a truck full of trucks. However keep in mind attack craft (and Chaos have lots of carriers), Lightning Strikes (watch out for Khornate ships) and ramming (general Eldar concern against all opponents, but Chaos maneurability makes them better at ramming Eldar).

I ban you cus thats okay, the people of the justice under my command will receive my godly blessings. I shall not sacrifice any soul to deal with the evil !

I ban Michael 'cos, right, for justice and hope, avoid direct confrontation with the evil by way of godly blessings. Just as planned.

I ban you cus evil cant be wiped out, indeed, but it can be made into a small insignificant force, and there shall be peace for a thousand years !

I ban Michael 'cos, in a way, the Imperium can't be fully destroyed - in fact, it is actually needed. Xeno threats are either already rendered insignificant, about to be rendered insignificant, or can't be destroyed outright. But thousand year of peace? I doubt that your big blue benefactor will like it, afterall, he'll be risking to cease to exist.

I ban you coz I hope the Imperium will fall.They killed millions of innocents for wiping out dunno hundreds of "heretics",which might be just some people,who think in another way.The Imperium stands against the evil,but it will be or it is already the reincarnation of the evil,in fact the only ones who have a chance against the Chaos Gods and Chaos supporters WERE the old Elder.Whatever as I probably mentioned before the Tau should be successors of the Elders,getting even further than humans in technology within 5000 years,instead of 45,000 years and are more intelligent and slaved the Kroot is impressive.So,there will be never peace.

I ban Destructor 'cos, do you know why there will never be peace?

Because of Orks. All Orks are latent psychics capable of subconsciously altering reality to their beliefs, the more Orks there are that believe in something, the more impact on reality they can cause.
Orks form about 90% of all sentient biomass of the galaxy, and EVERY SINGLE ONE OF THEM thinks war is the only way to exist. And considering that it is essential for Orks' reproduction, this entire situation can and will only get even further.

Finally, the old Eldar actually created Chaos. 1/4th of it, anyway, but it was the 1/4th that caused the fall of the Dark Era of Technology mankind. Which gave Necrons a run for their money in terms of tech.

As about Imperium's overkill policy, would you rather take any chance with Chaos? Or let Tyranids claim all biomass of a lost world? Eldar in particular know one does not take chances with Chaos; e.g. sometimes Asdrubael Vect has to quarantine and purge entire sections of Cammoragh when another Dysjunction hits his gigantic cesspool of a city.

I ban you coz didn't I kill Asdrubeal Vect in DoW:Soulstorm?

I ban DN 'cos, nope. Firstly, Vect was known to use body doubles (source: Path of the Archon by Andy Chambers). Secondly, Haeomunculi can ressurect Dark Eldar VIPs assuming they have a body sample and the VIP isn'd dead for more than a day. Thirdly, at that point Vect was a character in tabletop game and as such his survival doesn't need to be explained, it is just assumed he lives, even if he gets a Deathstrike Missile in the face.
Finally, Tahril says that if Vect would be killed, he'd taken his place, implying that wasn't the case.

I ban you cus thats an interesting convo, luckly no spoilers

I ban you coz I think got a point.And now back to your Orks...there are just cannon fodder,except for Waaghbosses or other Bosses.And there even declare war to themselves,I do not think there a big thing.Although in greater amount it could be critical.

I ban DN to remind you, that upon death, an Ork releases spores that will eventually grow into MOAR ORKS (well, more orkoids, anyway, squigs, snotlings and gretchins too). Means that the more they fight and die (especially with each other), the more of them there are, and the more impact their subconscious psychic abilities can cause on the Galaxy. And there are already so many of them that there are entire regions of space held by orks neither Imperium nor Abaddon the Despoiler can even hope to reclaim.

This can be played around a bit; Ordo Xenos and several IG regiments (e.g. Valhallan Ice Warriors) know about this and usually burn Ork corpses; however, a planet that once was attacked by Orks but was reclaimed will likely suffer repeating feral ork incursions in a few years (source: Ciaphas Cain series by Sandy Mitchell - the first 40k books I have ever read, and worth their time). In addition, Crons and Nids have a way around this.

I ban you cus I see the point in exterminatus now, just go in those areas and wipe them off together with the planet. Protoss style.

I ban Michael 'cos surprise surprise, Orks have spaceships too! And in enough numbers to not let any other ships anywhere close their most fortified worlds.
Then they'll loot everything they can and something they can't from wreckages of attacking ships and build more ships.

I ban you cus throwable junk bricks cant be counted as SPACESHIPS. Not like we cant just cloak in, pop right above the planet and it goes KABOOM.

Maybe some of those kiddie races can do something as simple as a death star... I would personally go for THIS:

Let them have as many ships they want around the blowing planets, to go off like fireworks.

IF tech really goes advanced mode, there are ways to wipe off life on a planet without destroying the planet, like the protoss prison ship wiping zerg from under it. That was beautiful.

I ban Michael, imagine Blood Axes kommandoz infiltrating and looting your Exterminatus weapon (most of those wipe out all life on the planet, e.g. Virus Bombs). Counter-infiltration systems blah blah blah, Ork psychic powers and blessings of Gork and Mork invalidate them. There was a case when a bunch of Kommandoz stole an Imperial battleship and navy command learned about it only in a few months or so. To steal a Planet Killer would just need moar Kommandoz.
Then their boss declares WAAGH and rolls through half of subsector stompin' whatever planets got in his way flat.

I ban you coz Orks with Exterminatos Torpedoes is pure madness!!!

I ban you cus orks are too stupid anyway

I ban Michael 'cos, probably, but they have an intuitive understanding of technology, and sometimes pull out tactical moves nobody else expects because "blah blah blah orks are stupid".
Besides, Mekboys, some Weirdboys and Blood Axes are smarter than other Orks.

Sometimes, however, Orkish psychic powers against them. For example, Commissar Yarrick is believed by Orks to be a sort of immortal boogeyman - and in 7th Edition rules, he has Back From The Dead (remember Living Saint from Soulstorm?), Toughness 4 (e.g. he's as resilient as Space Marine) and carries a Storm Bolter in one hand (he lost another hand in a fight with a Warboss and replaced it with a Power Klaw he looted off that Warboss), and that dude is far past his prime.

I ban ya coz that isn't even the worst,remember the Space Hulk form Battlefleet Gothic : Armada with the Exterminatos Torpedoe?It was very tricky to get him.