I play only caster roles and all my jobs (including blm) has a healing spell in the hot bar.
A great caster will know when to throw a cure to save the situation and it has nothing to do with healers being bad.
Sometimes someone makes a mistake (tank, dps, caster, healer) and without everyone's input it can lead to a wipe.

I think more people should see outside the box and help other roles when they have a moment.

For example, I always cast Dots on mobs when I am playing healer. I am not going to stop doing that just because it is not exactly my role.