This debate is like the fashion industry; it generates its own momentum for no real benefit other than its own.
Movies and movie stars don't exist in a vacuum. Do people really think that the actors, directors, and producers are not aware of the (rumours about the) sexuality of their stars? They react because of concerns over how we will react. And how should we react to this non-event? We shouldn't.
If he were a one-dimensional movie action hero actor, he might have something to worry about because the perception is that that core audience is driven by machismo but none of the modern action hero actors have that much longevity in any event these days.
Quinto has appeared in successful TV shows, movies, and plays but he's not an A-list movie star. He's not a go-to guy to carry a Hollywood movie (Bradley Cooper is getting there for example but Quinto is way behind). There is plenty of breadth in his career and if he never got another Hollywood movie again he'd still get plenty of work. The guy has presence and talent.
FYI: Being a bad-tempered, drug-addled lunatic affected Rupert Everett's career, not being gay. Once he put that behind him, his career was revived - and he's still very gay... and ridiculously posh.
When asked, Tom Hardy openly admitted having gay relationships in his youth - he didn't back-pedal or retract as far as I'm aware. He simply pointed out that he was married to a woman and quite happy thank you very much. I think he was iritated by how much airtime the casual remark generated. Further, he made it quite clear that homosexuality and bi-sexuality is quite common among actors!
Sir Ian McKellan does just fine. John Gielgud was a renowned actor and they don't come much gayer. Nigel Hawthorne was 'outed' in the papers but he was rather irritated by all the fuss. He'd never made a secret about his lifestyle and had been attending functions with his partner for years. Everybody in the industry was aware and the papers made it out like it was a big secret to try and big up the story.
To summarise: I want Quinto's babies. Everybody back off.