I play blitz in part to learn how to play under time pressure. I can't do that if you relieve the pressure whenever my clock runs low.
Also, I play rated games. Rated games are supposed to be at least a little serious, and so I feel they ought to have some basic rules of decorum: no takebacks, no added time. If you add two minutes to my clock and I win the game, my victory feels cheapened, much as it would be if I had to take back a move. Exceptions can be made to both of these (in the case of obvious misclicks in the former, and obvious disconnects in the latter), but they should be just that: exceptions, not the norm.
You might think you're being polite when you add time to my clock without asking, but you're not. Please, ask first.
Also, I play rated games. Rated games are supposed to be at least a little serious, and so I feel they ought to have some basic rules of decorum: no takebacks, no added time. If you add two minutes to my clock and I win the game, my victory feels cheapened, much as it would be if I had to take back a move. Exceptions can be made to both of these (in the case of obvious misclicks in the former, and obvious disconnects in the latter), but they should be just that: exceptions, not the norm.
You might think you're being polite when you add time to my clock without asking, but you're not. Please, ask first.