There are tons of people, myself included, who don't use HR monitors or other devices when running.  People shouldn't be disallowed from the leaderboards just because they don't buy all the extra gadgets.  Additionally, that would rule out anyone who uses the Strava app on their phone and I doubt Strava would want to do that...  

I wish there was a way to flag more than one at a time, but right now, we are stuck just flagging each activity separately.  I usually use up my allotment of flags each day (typically 10/day) cleaning up local segments.  The good part is that when you clean up one segment by flagging the bad activities that are clearly incorrect, you actually end up cleaning up others nearby since those same activities often cover a number of other segments too.  I've advocated for Strava to implement local moderators (or something along those lines) that have additional authority to flag more activities.  They would have a better idea of local situations and could really help to keep segments in their area in order.