I believe that the bottom line is that everyone is entitled to make their own decision about what they do in any given situation. I think the problems arise when we start applying our views on what is right in a gaming situation to others. If someone feels that remembering to do your own stuff is an important part of the game and wants to play strictly rules as written, that's a matter of personal preference and noone should label them a jerk or yell at them for it.
To put it another way, if you forget a trigger and your opponent offers to let you go back and take it, (or doesn't), then accept it or decline, but don't feel bad about it. If your opponent misses a trigger, then remind them and let them go take it (or don't) but don't feel bad about it.
To me, that's what "Fly casual" means. If you want to play strict, fine if you wasn't to play loose, fine. I might not like it, but meh, whatever. either way, you're not a jerk.. f you think your opponent is a jerk, you probably need to look in the mirror.
Of course, if they expect second chances but won't give you any, then yeah, they're a jerk. Sorry. Put up with them or don't play them.
Edited by adder