>>712936369 (OP)Not every Eldar is a raging retard, some of them do actually understand the idea of cooperation, and they generally hate chaos more than anything else. Imperial/Eldar beef is mostly a product of bad writing to begin with. Dark Eldar, sure, fuck 'em, but craftworld, exodite, and harlequin Eldar really have no reason to not be at least on speaking terms with the imperium, except bad writing.
Tau are pretty receptive to working together to take out the serial killers of the galaxy.
Kroot don't give a fuck and are happy to work with whoever is arming and feeding them. Also they like not being dead, which rules out most of chaos, tyranids, and orkz anyways.
Votann are basically imperial anyways, pretending otherwise is being silly.
Necrons are usually pretty omnicidal, but some recognize that chaos or nids are a much more imminent, immediate problem that needs to be dealt with at least before everyone else. Some necrons outright just don't have a problem with the local wildlife, as long as it stays off their lawn.
Orkz and Tyranids basically can't be negotiated with, only directed at someone else. Time will tell of Ghazzy can bring about a new age of greenskin diplomacy by ascending to a Kroark.
Everyone hates chaos, everyone hates tyranids. If it's against chaos, orkz, or tyranids, there is basically no reason everyone else wouldn't be on board to cooperation. The only diplomatically risky faction is the dark eldar, who everyone BUT the Eldar want dead.
This also rams into the derp of the inquisition. The inquisition is, in fact, not completely retarded except around the Grey Knights, which are distilled retardation.
Most inquisitors are made to answer for calls to exterminatus, and many actually lose their title over doing it wastefully, if they can't prove the real threat to other worlds that leaving this one as is posed. Many inquisitors, in fact, work with these xenos because of the net benefit to the imperium these interactions cause.