Assumptions are always dangerous. They are, after all prone to being wrong.
But... On the whole, assuming people are heterosexual isn't that unreasonable. Most are.
Estimates vary on how prevalent homosexuality is, but even with the most extreme estimates (which suggest something like 1 in 4 people is gay), it's still a minority.
On the whole, more likely than not, the people you see ARE heterosexual.
But... As with all assumptions, sometimes you'll be wrong. And you simply have to be prepared for that if you rely on assumptions to any degree. (And everyone does... Not making assumptions and generalisations at least some of the time is nearly impossible.)
So... No, it's not wrong as such, just... Be aware that it won't always be correct.
But... On the whole, assuming people are heterosexual isn't that unreasonable. Most are.
Estimates vary on how prevalent homosexuality is, but even with the most extreme estimates (which suggest something like 1 in 4 people is gay), it's still a minority.
On the whole, more likely than not, the people you see ARE heterosexual.
But... As with all assumptions, sometimes you'll be wrong. And you simply have to be prepared for that if you rely on assumptions to any degree. (And everyone does... Not making assumptions and generalisations at least some of the time is nearly impossible.)
So... No, it's not wrong as such, just... Be aware that it won't always be correct.