As standard, any rides you upload to Strava are public anyway. So there's a variety of ways to view other people's rides. eg if they are in a club, you can view the recent activity for that. Or check the results for a segment, you can limit that to the last day or week etc. You could create a segment for the road outside your house, then identify everyone passing by.
So the flyby feature doesn't really change this, it just makes it more obvious.
You can set all of your rides as private, but then you miss out on most of the social features on Strava. eg segments, or challenges, or your followers seeing your rides etc.