I started playing HoN without having ever played DotA, but thankfully I did so with a bunch of friends, many of whom were also unused to the game's style, so there weren't any problems with that. But I read as many tutorials as I could while downloading the game, so when I got a grip on what the terms meant I already had somewhat of a base to work on. I still got raped over and over again by those of them who had played DotA, but I soon started getting better, and it was all private games, for fun.
The problem with this game is, as it has been mentioned, that a single "newb" can ruin the experience for the whole team; it starts with the newb dying a few times (and it really doesn't take all that many) and it ends with every member of the team, regardless of how good, getting mutilated by the other team.
For those of you who never played DotA or HoN, to get a broader scope of the situation, every kill gives you a certain number of points to spend on items, and killing other players gives you quite a substantial amount. Those items can make you really powerful, so teams have to have a certain balance in terms of items to be able to stand up against each other.
Now you insert a newb, you get one team racking up points easily, buying powerful items, and when the rest of the team tries to fight them, they're way too weak, item-wise, to be able to stand a chance.
That's why HoN doesn't have much of a newbie-friendly community, particularly when playing in ranked matches. That's no excuse to do what some of them do, of course, and newbies should always be given a chance. On the other hand, especially in games like this, you should try to read the tutorials before going into the game, and if you get kicked out of games a few times, don't worry too much, it happens to all of us. If they keep insulting you and bothering you, though, you could always attempt to report them or something.
Well, that's more text than I expected.
tl;dr: Newbies should always be given a chance, but try to read the tutorials. And it's kind of understandable in this game, more so than others.