Do you think it's important to have good manners?
Yes defintely, just a few words can make the world of difference showing appreciation, gratitude or apologies.
If yes, why?
I think it shows that someone has resepect and that they are civil, it's not hard to use basic good manners and they are a universally recognised code so they should be used.
Would it bother you if someone didn't have/ use basic good manners?
Yes, especially if I used good manners towards them. I would assume that they are rude and ignorant. It' something that really bothers me actually when people don't use basic good manners.