Low birth rates aren't necessarily the outcome of the problem as the two aren't exactly always connected, and even then, it wouldn't be the cause so much as a byproduct of that if proven beyond doubt.
Like Spartan says, I and most other males don't fear marriage because we are adulterers in waiting, but because divorce is just too easy these days and marriage isn't seen as a serious commitment by woman or men for that matter anymore.
I could build seven fortunes, then get married...And yet, a year or so later a divorce could be filled against me for any number of reasons, and I would suffer losing a majority of that hard work, all because someone didn't see marriage as a commitment between two individual's to work through together, so much as a state made contract easily exited when it benefited them or they grew board of their partner.
And it's not just Men that suffer this, some men treat women in just as abhorrent fashion for just as bad reason's it's just that the system is less likely to gift rewards to them over female divorcees.