It is impossible to realize your proposal. You are forcing some people to change specialization because your opinion is; too many healers is not ok. this is an opinion and not a fact, which immediately invalidates your point of view. Suppose this is still observed then it means to me, for example, that in the evening hours I am almost forced to play a DPS because the teams are too 'strong' in your opinion. This makes panda-wow no longer a 'free' game for me.
Don't get me wrong, I get where your thought process is coming from. Sometimes we are in a battleground with a total of 6–7 healers during a 15v15. But as Nyancat says, as soon as an enemy team deploys a double affliction warlock who knows how his rotation works, you are immediately lost with only 1–2 healers.
Now imagine this being deployed effectively, how many people do you think would have been helped? And how many do you think would have been lost because of this decision?