As a healer, I would say thats on the healer for being a jerk, not you for speaking up. Anyone who ditches a duty from someone saying they're new is likely to ditch it the moment someone screws up.
In op:s case then this is why its good to be a healer.
Dont be afraid of tanks that are rude or in a hurry, he wont get far without heals so you just got to standup for yourself and tell him that your new and not comfortable with large pulls and either he accepts that or he can take his 30 min penalty and leave.
Yeah, I want to tell first timers what to expect when they go to a boss and the tank just goes straight to the boss and doesn't give me a chance to let the first timers what will happen. Or when they get to the last boss intro the tank ignores it and runs the risk of the first timer getting locked out. So yeah that is a problem indeed.