I think Speedos are really to much for men to be wearing at public beaches. Yes, woman wear suits similar to speedos but on them there is not a whole lot for imagination. It is a flat surface, though perhaps they could wear a bit more as well.
However on a man you get well, a different view. Which to me leaves very little to imagination. It isn't that I am trying to look but its hard not to notice. The saying, "can't look away from a train wreck" comes to mind.
I'm surprised that this is even a question. Wearing a speedo is like saying you want to wear virtually nothing at all. I think bathing shorts are just right for the gents.