rather than rebuke people try and convert them first, if it seems incurable THEN rebuke them.
but seriously, in addition to what an above poster said regarding the openness of classes, you should also take into account that in the beta people will hardly know which classes will truly be "best" at what. Anything people could say right now is either only relevant to the start of the game, or guess work at the endgame.
Also, since you can do literally everything on a single character, don't worry about mistakes! Don't like your class change it, don't like your stats respec them, your craft doesn't feel like its helping, do a different one. The only thing you cant change is your character, so make sure you make one you will like looking at forever and a day.