Well, let's put it this way. Obama announced his support for marriage equality in May 2012, and managed to win the next election with only a slightly reduced majority. Not that most of his supporters were neccesaarily voting FOR marriage equality, just that they obviously weren't voting AGAINST it.
Before Svend became the first openly gay MP by announcing the obvious many of his advisers said it would cost him votes and they needed his voice so don't take the chance. The next election he increased his winning margin because people like politicians who are willing to stand for what they believe in even if it is not the majority view.
I remember when that happened very well. Later that week, I saw some old Tommy Douglas campaign signs tossed into someone's garbage can(in Edmonton). Obviously, he'd been hanging onto them since at least the late 60s, and just coincidentally chose that week to toss them out.
But I agree, it didn't hurt Svend or the NDP very much at all, in the big picture.