When I find myself thinking of something during meditation, I try to reestablish my focus and in the process I just drop the thought. I think that's correct during formal meditation, but dropping an unpleasant thought after noting it in daily life is wrong, as it leads to avoidance.

I agree, that's something to be careful of. I think it depends on what kind of formal meditation practice you're trying to do. Concentration meditation (such as zhiné from Tibetan dream yoga) encourages you to focus solely on the object in question and to let thoughts drop. Apparently that trains a different part of the brain than does mindfulness meditation. (See The Clinical Handbook of Mindfulness, Destructive Emotions, and Mindsight for some of the research behind that claim.) Formal mindfulness meditation focuses on just being aware of thoughts as they arise without getting "sucked in" such that you lose awareness of your surroundings. My own experience with this has been that ugh fields and related phenomena seem to become much, much easier to notice as a result of mindfulness meditative practices.