i never said competitive environments didn't have shit talk. i played almost every sport in high school and you are right, every single one of them had a lot of shit talk. but i wasn't sitting around in practice thinking "oh man i better run a few more laps because i don't want the guys on the other team to make fun of me." lol that would be a pretty silly way to go through life. you practice simply because you want to be better. you want to be better than the safety that's covering you, and you want to be better than the other wide receivers on your own team (who aren't talking shit to you). you practice because you want to win because you are a competitive person in the first place.
but what if you're a competitive person who just can't find people to compete with? it's hard as hell to find decent gg players to practice with and try to progress. so you try to get new people to play and increase the player base. now normally my friends and i love to talk shit when we play third strike. it's funny as hell and i love it... but when i try to teach them how to play guilty gear and they are still trying to get past the basics, talking shit to them just makes them want to go back to playing 3s or cvs2.
the bottom line is if you aren't already a competitive person who wants to win, talking shit is not going to motivate you into becoming a competitive person. i do agree with you however that it can help some already competitive people get a little more motivated, but only some. the bigger problem is that in the US most people don't even have anyone to compete with on a regular basis. it doesn't matter how bad you want it, if you can't find the competition to play with consistently, you're just not going to get better. and talking shit while trying to recruit new people is pretty counter productive. the japanese players aren't talking shit to us, yet people here want to beat them don't they? why is that? because they crush us. they show us that there's a much higher level and that we aren't there yet. they motivate us just by being better, not by talking about how bad someone's video game skills are on a forum. talking shit is fun, but it's not that important for upping your game.
i am curious though... how much shit talk is there in japan?