I think the main issue isn't so much if healers should DPS so much as how much they can. If it was a case where healers heal most of the time, sneaking in damage spells here and there, it wouldn't be as bad. But in most content, even Savage, so long as others don't screw up, a healer needs less then half, maybe less then a quarter of their uptime to heal. So, basically, I can be in a situation where 80% of the time I only use 10-15% of my skills (healer DPS), and just 20% of the time do I use 75% (teh healz) of my skills. And that...is mind-numbingly boring.