I would try not to take it too personally - these people are generally uninformed.

Since swapping from SCH to WHM in SB I haven't had to deal with this nearly as much but during the process of leveling SCH I did encounter a few of these ASTs. I just let them solo heal. It was generally fine (maybe with me tossing out an Indom or a Lustrate and still using fairy abilities) and the few times it wasn't I would explain to them after a wipe.

If they swapped, cool... if not, I'm not there to carry them through their own ineptitude.