Popper's idea on the subject is ultimately borne out by the end results of the "you're entitled to your opinion" attitude; something designed to promote positive discourse has since been hijacked by fringe elements at everyone else's expense. You see this with the anti-vaxxers, the climate skeptics, and the "alternative facts" crowd.
Really, the answer becomes; no, you aren't entitled to an opinion you cannot substantiate. We should not respect viewpoints that have no solid backing, we should not tolerate viewpoints seeking to undermine the institution of a tolerant society either.