I don't mind people drafting me while commuting, if they can also come forward for a spell, so much the better so we both get to work/home faster.

A big difference with random people drafting me to being on a group ride:

1. I will not signal for them nor call out
2. I won't wave them forwards or otherwise acknowledge them
3. I will look to drop them if I can (only through raising the pace however, not by being sketchy or taking risks)