These questions are less of an issue for an academic conference, where the goal is to have people present their work and ideas for others to wrestle with and discuss. The skill of the presenter may have a great deal to do with how convincing he is, but has very little to do with any decisions about whether he should be invited to another conference. That has more to do with the quality of his work and ideas. The only exception might be if his ideas are simply offensive or ridiculous – racist, homophobic, denying the existence of the planet Jupiter, etc.. And even ideas that seem offensive need to be taken seriously if they are based on facts that can be proven.