Lori- it sounds like you are a very good leader and do not avoid the role of leader, even if it means ruffled feathers. I wish all meet-up groups had good leaders. I probably should try them out again. Are you the primary leader in your group or does everyone take turns at leading?
I have meet many "loose" groups out on the trail with members spread out all over and many "where's Joe?" comments. The weak members are left behind. Many of these are quite young (college students maybe?) without anyone appearing to be very experienced.
I just make it clear I want to hike with a particular kind of backpacker for one trip or another - the leadership is more a matter of deciding who's going. One of my main tactics with meetup groups (I have two, and yep, I'm the primary organizer in both, but lots of event hosts in each) is being very explicit up front and then guiding the newbies away from certain trips before they get in over their head. Once on the trip I kick back and let group consensus take over, unless someone gets hurt (it's happened on other people's hikes, not yet on mine, tho I did end up sending someone home from a SAR training exercise once...). The group usually pitches in on the few instances where someone's got a bit off and we can't find them.
Some of my organizers are Sierra Club leaders, others have experience leading high school backpacks or other sorts of groups. Some just turned out to be pretty good at setting up events.
Most of the lost folk I meet on the trail are as you describe. Lots of them I find on the Mist Trail... Pretty much anywhere in the national parks on the most popular trails, there's loosely organized groups looking for each other. I'm surprised SAR isn't out there more often.