There are two competing schools of thought concerning flagging. One maintains that flagging is poor sportsmanship, the other considers it a valid strategy (I belong to the latter). I don't think there will ever be consensus on it.
Now, bullet is a special case. Up to a certain level, bullet is almost entirely about beating your opponent on the clock. If you do not succeed in flagging your opponent, you'll be the one to be flagged. I do not see how it appeals to some low rated players, but apparently it does. But if you want to improve as a chess player, I'd suggest staying away from bullet.
I have heard that flagging in chess when you are in a losing position is generally frowned upon, but is this the same for bullet chess as well? I normally only ever play bullet since I don't have a ton of time to spend on chess, but a large majority of my wins are by flagging, and my accuracy is very low. Is this something that I should try to stop doing if I want to improve, or if not for that, just out of courtesy?
Thanks!