Well, there are some assholes online, no doubt. Like every online gaming community, we have our share of rude people. However, while the form in which they made you leave is totally unacceptable, you should understand it's a team game that relies on balance. One player having virtually no MP experience on the team will, in all seriousness, mean that team will lose.
The solution? For the moment, host your own games (preferably entitled "noobs") or just join "noobs only" sessions (that said, I wouldn't recommend joining such games hosted by Cambokill and Jojo-Effect, unless you like being farmed for stats, that is ). Gradually, you'll get more confident and more comfortable with the Demigod MP. Also, the players will start to recognize you, and if you are half-decent, they will accept you gladly. I started playing DG in October, and actually have no problem participating in "skilled players" etc. games now. Much to my surprise, some pro players are actually pming me to join their games if they see me online, even though I'm not that great. So in a nutshell, the formula of success is pretty simple: be a reliable teammate, don't rage-quit, don't trash-talk, don't try to play on the winning side exclusively (it's not always possible to balance teams perfectly), try to get better, and you'll be fine. People here will respect you.
There are some pro players that are really friendly to newcomers and usually don't mind coaching noobs/playing on weaker team: first and foremost, I'd mention Pacov (CheesusCrust), renz0kuken, rawrr (4nana), Darkliath, brasher_01. Feel free to pm me here or in-game if you need more information.
Don't get frustrated. A little bit of patience will pay off