The slimiest 'slimy trick' -- true intellectual dishonesty -- to me seems to be the one Alinsky said is required by any movement, and particularly any reformist movement: demonise the enemy. This is generally done by basing praise/condemnation on the actor rather than the act. The left does that a lot. The right does too, but I find it hard to expect better of them.
I think we would do better, and be more honest, to leave off complaining about the acts of NATO merely because they are NATO's acts, and switch instead to illuminating US and NATO hypocrisy. Hold them to the ideals they claim. When they point to the Kosovari as justification for bombing Beograd radio stations, then we should point to the Kurds and ask loudly and repeatedly 'where are the bombed radio stations in Istanbul?'.
A person is not less dead, nor their family less traumatised, because killed while in uniform than while going to their civilian job. Most in uniform have no real choice in whether to wear it, or whether to use their weapons. Milgram's experiments demonstrate that conclusively, imo. We shouldn't be killing the folk at the bottom of the exploitative food chain.
Our criticism, it seems to me, should be directed at the slime in power, who have a disgusting habit of protecting slime in power elsewhere. Thatcher resp. Pinochet is an egregious example. The US and NATO should be focusing on turfing out Milosevic and his ilk, and replacing them. We should criticise them strongly for not doing that. And we leftists should be concentrating on turfing out those who believe in the exploitation of the many by the few. They are our natural enemies, not NATO qua NATO.
Or is our real goal only to be always in opposition?