I can't speak for other men, but when I was single I almost never went without barriers until I'd been involved with someone for a few months and we had both been tested for STDs. Partially it was fear of STDs, but it was mostly rooted in a fear of causing pregnancy - once there is a pregnancy it is no longer up to me to decide how or if things progress. What happens in a woman's body is her business unless she chooses to include me, which is not certain and must be conditional (on my not being an asshole, for example). My only point of agency in that process was in choosing to use a condom, and I did so very rigorously.
I've had a vasectomy and would follow the same rules now, were I single. If there had been a RISUG option around when I was done making babies I'd have used it (it is always nice to be able to change your mind later). Whether someone believes me or not is less important than the fact it provides me with some control over the outcome.