(Sorry, accidentally submitted that early!) However I also think that there are doubtless instances where consenting adults could make incestuous/polygamous marriages work successfully to a point where they are comparable to heterosexual marriage, (which seems to be the standard measure) So I would also be ok with both if certain criteria would be met.
It is a complex issue.
Thank you for the rep. Just to clarify, I don't support either incestuous or polygamous marriages. Nor do I feel that anybody is being unreasonably discriminated against if they remain illegal.