payn
Glory to Marik
Some editions of the game make the gulf between optimized and not quite large. So, I get some of this statement, though how folks treat each other is huge. Most of the stuff in the OP is just awful.If the campaign is about effective combat characters defeating dangerous foes, then building a combat-weak character is actively undermining the campaign ethos, and so is "the wrong way to have fun", because it hurts other people's fun.
And, TBH, most traditional D&D style games are about effective combat characters defeating dangerous foes, so you should build at least a competent character. Your GM should make it clear whether or not the campaign is going to require optimized characters.