The intent here is not in any way to silence complaints or criticisms, but to ask that players that have them take the time to be specific, provide details, and be constructive. It's not "long list" that's the problem, it's long lists that don't take the time to be constructive. So, in short, if you take the time to provide thoughtful feedback, you don't have anything to worry about - that's the kind of thing we value.
One of the most common criticisms we see is that the forums are ugly and that trolling and negativity drive away players who DO want to contribute constructively. We want the forums to be a friendly place to discuss the game, and we want to protect players that want to use them that way. That doesn't mean we want to eliminate negative feedback, but we do want to cut down on the insults, hostility, and other behaviors that sometimes make the forums inhospitable. We want to encourage people to provide us with useful feedback that we can take to the developers. We also want to remove people who are just here to insult others and bash the game for entertainment.
I think you've just given yourself enough 'grey area' to ban pretty much anyone.
When players encounter a bug or a source of frustration, not all of them are as keen to the forums as you may think, and will often post in frustration and anger. I think your new policy insisting players be "specific, provide details, and be constructive...or face bans" comes off as quite threatening.
I'm all in favor of cutting out the trolls, the rude people and anyone touting GW2 (or whatever the fotm MMO is), but to threaten people for posting about an issue that draws them to the forums to begin with is just silly. Not everyone who posts cares what your rules are, they may simply be upset by something they just encountered and they came here to tell you about it and complain about it. Every complaint, no matter how it's phrased, should be valid to you. Every CUSTOMER should be treated with some amount of respect by you, not threatened for not having a 'constructive' enough complaint. Threatening to ban an already upset customer just seems entirely counter productive to me.