Someone told me today to stop using DPS spells like Stone

[Rongway]

The three most important rules of a healer
1. In terms of keeping people alive, you are the most important followed by your mt and co healer

This is untrue. The most important person keeping anyone alive is themselves, regardless of their role. That is to say, people need to do mechanics so that they don't make unnecessary extra work for the healers.

It's not the healer's job to heal avoidable damage. The healer's job is to heal unavoidable damage.

If the healer and other party members know each other well enough, someone might eat an avoidable hit in order to do a significant amount of extra damage, if it won't create extra work for the healer. But if you don't know the healer personally, don't assume that it's okay to take avoidable damage.

Again, it is not the healer's job to heal avoidable damage. The good ones will heal it because a dead DD does less damage than an irate healer who had to waste a GCD on someone being selfish. But it is not their job to do so. People need to do mechanics.