I've done group rides off and on since last summer, though nothing over 12 riders. Winter is just about done so our group rides are picking back up again. Hasn't really been much concern, and we ride easy and hard and the like.
For this, I leave it up to each individual. If you want to ride with a group, go for it. If not, no worries, there, either. Being outside and constantly moving doesn't seem to pose much, if any, risk in my opinion. The MD that rides with us has stated as much as well, but choosing to ride in a group or not is such a nonissue that I don't think there should be much consternation about it.