I've ran into a few of these large "meetup" groups before. For exactly this reason I don't participate. What I don't understand is with 17 people why you couldn't leave 1 or 2 behind with the slow/tired hiker to make sure they are OK? This behavior is disgusting. They are random strangers meeting up for hikes with huge groups and zero responsibility.
I looked up the HVH "legal disclaimer" and it expressly mentions this: " There are no leaders on these hikes, you are your own leader- This is YOUR hike."
I would never leave someone who I set out with who was injured or further unable to proceed to hike out on their own. People who I hike with know this. There are more important things than getting to the summit, and making sure everyone in your party is OK is a must. Most of the time slow/tired/injured hikers will try to reassure you that they are OK. They will say things like "go on without me I'll be fine" or "I'll catch up". Chances are that they won't. If they're already falling behind for some reason, they aren't going to magically catch up, and likely they aren't fine.
edit: Kenny I wasn't really going to leave you on the top of blackhead that one time in the winter
Hike today, work tomorrow.