If you're playing alone, or playing a videogame, yeah, there's no reason you can't just do whatever you like. You're the only one who suffers the consequences. You're not playing alone, though. Roleplaying is a social activity; you do it with other people, and the goal is supposed to be fun and enjoyment on the part of all involved. Other peoples' feelings and comfort levels are involved. That changes things considerably in terms of what kind of "edginess" is acceptable and what makes you jerk for doing it.
If your character charges into the enemies and ruins any hope the rest of the group might have for a tactical approach, that affects *everyone*. They can try to rescue/help him (risking their own demise), or they can stand back and let him take the consequences of his action. If he grabs any loot he sees and tries to hide it from the party (because "my guy would do that"), understand that the others would be perfectly justified in saying "We don't want you with us - you screwed up the ambush and stole from us." and walking away. Or killing him and leaving his corpse for the carrion eaters. If YOU are entitled to only consider your own needs, so are they.
There's a knack to playing with a group. The GM is off, imho, to an excellent start with her social contract. The discussions on this list are also a good beginning - it's a chance to discuss viewpoints and expectations. I do get the impression that your experience with group cooperation is somewhat limited. Cooperation does NOT mean just rolling over and letting people bully you. It DOES mean taking into consideration that everyone has needs, desires and expectations, and if you don't want to consider anyone else then you can't expect anyone to consider you. Also - cooperation is not "communism", nor does it mean no conflict between characters. It does mean keeping the group objectives in mind, and treating others no worse than you would like to be treated.
From your postings, it looks like YOU want a fighting-oriented, fast advancing, statistics-heavy, every character for himself game. Your problem here, as I see it, is that looks like NO ONE ELSE, especially the GM, wants that game. The irascible loner is a great protagonist in fiction, but a RPG campaign as more like an ensemble TV show. It's not starring any one character, and the drama comes from overcoming their differences and incompatibilities to achieve a greater goal. The focus will shift from episode to episode, but everyone gets their time in the spotlight (and their share of the goodies).
Being a part of a social group (and a game is certainly a social group) invokes a host of conflicting, unwritten expectations. Talking about them is at least a way to get them out on the table so we each know where the others are coming from. It also involves constant compromise -- from everyone. When there are points that can't be resolved and make the experience Not Fun, *then* is the time for somebody to walk away.
Most of the players in the group are working adults with a lot on their plates. Most of them, as you observed, are ROLE players, and are looking for a cooperative, story-oriented style of play. If the game isn't fun for them, they'll walk away -- including the GM. Remember, if the GM ain't havin' fun, ain't nobody havin' fun. You might "win" by virtue of being the last person in the game before the GM quits.. but what kind of victory would that be? It sounds, from your posts, like your preferred play style is pretty much totally opposite -- but -- have you ever *tried* the other way? With people who know how to do it very, very well?
Give it a try - you may find that it's more rewarding than you expect, in ways you don't anticipate.