Valid points in many cases. But my main point was that they're not universal. So, looking at those ones one at a time:
getting out of the dungeon faster: A help if you want out quickly. But there are some dungeons I've run many many times over and never really gotten to even see what they look like because we were always racing past everything. It'd be really nice to be able to stay a bit longer and get the time to really see them once in a while.
less mechanics to do: The mechanics are the fun part. It's boring to just burn through every boss the same way. Plus there's the fact that many of the dungeons whose mechanics are now routinely skipped are low level learning dungeons designed for teaching new players how mechanics work. The biggest reason why so many players end up in endgame (or at least late game) dungeons totally clueless about how to handle mechanics is because the simple version of those mechanics are too often skipped in the earlier dungeons that are supposed to be teaching them.
less chance for people to run out of cooldowns/resources: But in a long fight, most of your cooldowns will come up again. And a lot of conservative gameplay focuses on making sure you're recuperating your resources as fast as you use them (though a lot of that is coming from the damage dealers' support skills rather than from the healer).
less chances to make mistakes: Some people in this thread have been advocating that healers are best when they're pushing the edge, getting in every possible point of damage they can manage, skirting the edge of letting players die without quite going over that line. That approach is creating more chances for serious mistakes, not less.
(Note: This last argument applies only to the drive to maximize healer DPS, not the one about wanting healers to do a bit of DPS in downtime when they'd otherwise be idle. I don't really have any problem with the later.)
Ok, yes, I can agree with these. We could add debuf utility along with helping meet DPS checks as cases where it's useful.