I agree with you on this point, but you must concede that there is BFMing the rules, and there is blatantly disregarding the rules. BFM to make the mission happen and kill bad guys is usually acceptable, so long as you have three legs to stand on. If you can point to A) the book B) the mission results or C) sound judgement, you are probably going to win. But if you can't identify any sort of legal or results based reason for doing something other than "It sounded fun" you're probably going to get hung out to dry if you haven't already killed yourself in the process.
Momentary deviations from a briefed altitude are one thing, but knowingly and willingly deviating is a different animal. You said you wouldn't hook a guy for being 100 +/- 50, and I agree; however, I would imagine you would hook the guy for shacking 50' all the way along?