Would a Game of "Wicked Ones" Go Off The Rails Too Easily?
Potentially, no. I've seen multiple evil-character, monster-sort games run and most didn't fail due to the players they just ran out of steam or the DM fell victim to RPol attrition.
The ones I most recall were:
We were all kobolds who had had our settlement hit by dwarves. We were protecting a tiny band of survivors, barely had any equipment and our main job was to establish a new nest and rebuild. That one had a lot of potential and obviously, we were all supposed to hang together. Sadly, we lost the DM.
We were a band of evil and/or monstrous types sharing an enemy in the form of the lawful prison and the vicious prison guards who had trapped us and tormented us. That one ran for a good long time before we lost the DM, and I don't recall any serious player infighting, we just ran out of steam after our (epic) escape.
We were a band of evil/monstrous magic types coming together to start a guild in order to accumulate power. Everyone got on, with some potentially fun rivalry then one guy casually started murdering bystanders in the neutral town we were going to use as a base and the game stalled out.
We were a band of evil sorts of various kinds fully committed to overthrowing the new world order of shiny light and we had to work together because everyone else would kill us. This one also ran a good while, before we lost our DM (who was like, pathologically well organised). There was some friction and some party backstabbing, but not much because we all had much bigger fish to fry.
Oh! And there was one where we were all epic servants of some long-dead evil returned to the world and were scheming to bring them back. Because we were minions, we weren't allowed to turn on one another, but violent snark and a little light backstabbing were considered par for the course, as long as you didn't get in the way of The Plan. Weirdly, we all worked together like a well-oiled machine before attrition took the game down.