OP quote from comments:
No, once they said "if everyone become vegan we don't have space on earth to make food for everyone", the truth is that an omnivorous person take 18x space then a vegan because animals don't eat air. And that's the truth; when i say the truth, is like that, more or less, or like "you can't do sports if you're vegan" and look at me - i am healty and i do lots of sports and also there are some bodybuilders who are actually vegan. It's not preachy, nor a guiding principle, i am just informing people.
It is preachy and it makes you fair game for jokes. If all you had ever said on the matter is that you are vegan, the jokes would be infrequent and would fade over time. Once you start going into why your way of thinking is the best you invite discussion on your way of thinking.
For future mitigation stop discussing your beliefs if you do not want your beliefs being discussed. If coworkers continue to bring it up on their own, shrug and look bored. Don't engage them in this discussion and eventually they will get bored and move on to other things.
In response to the edit:
is it bad to have ideals? It is bad to start a debate on it? Maybe i think something that is actually wrong, but confrontation exists so that something good could came out, if it is done properly. Or should i get extra-informed and with that purpose really start debating - and so preaching - because i will held the notions of x people about it against the y of others?
No it's not bad to have ideals but it is a bad idea to start a debate on it if you don't want others making jokes about your viewpoints. With respect to getting extra well informed, you are the one who doesn't want to have these discussions so don't take part in these discussions. Criticism of others view points, however rational it is, opens you to criticism of your own. Don't dish it out if you can't take it.