Hopped on group finder for Hammer Station with my level 19 Sin tank. Both DPS were about my level, our heals was a level 16 Merc. While fighting the 2nd group right after the hallway turn, the Merc backs up too far and pulls aggro on the 3rd mob (the 1 with 2 elites and 3 strong) and we wipe. I asked him nicely to keep close next time if he was unfamiliar with the flashpoint. We rez and approach again. I ask for a cc. The Merc starts blasting me with his gun heal, pulling aggro on the group again, we kill most of them but wipe. Rez, kill the rest. I notice 1 of the DPS initiate a vote to kick me. The heals tells me to leave if I don't know how to tank. As I'm typing to make sure they know the heals messed up I am voted. It's probably best I didn't stay with such an oblivious group. I reminded myself afterwards about tanking Xeno II 16 man HM earlier with my guardian.
I play healers most of the time in every game I play. As my latest healer neared 50 I noticed that even in normal play, not missions, etc., that the npcs got smarter and jumped me when I would use big heals. Of course, so far, this has been true in most games. However, I would like to add that while I may have aggroed at the beginning from putting a HoT on my tank, I'm more inclined on that one to believe it was my activity in the aggro range of the npc that drew the attack.