@Rubis No offense, but you obviously have no idea what you're talking about from a game design point of view. Healers have always been survivable since Vanilla FOR A REASON.
Just listen to what you said. You already admitted that targeting the healer is the correct thing to do. Targeting healers IS what dps tends to do too.
You think you're frustrated now, try being everyone's favorite target. You already admitted YOU do it. Do you have any idea what it's like when everyone in the BG wants to single YOU out, all the time?
Healers need to be able to tank while healing because they get way more player-aggro than you. It's that simple.