Originally Posted by Drakevarg
My point is that they're not made out of any "evil" element.
That's one view, certainly, but as I said before if some one wants to decide that in their games negative energy is inherently evil, then that is also an equally valid option. The link provided by Saidoro
on the previous page summarizes the two extremes rather nicely, I think; we have negative energy as just another energy source VS. negative energy as a kind of tangible evil, and the subsequent effects of both.
I like to think that there is room for compromise.
The way I would probably rule it is that negative energy is not in and of itself evil, but since it is the opposite of life (positive) energy, it tends to encourage destructive actions (life is growth, unlife is destruction). A living being can use or utilize negative energy without instantly becoming evil because the positive energy of their life force balances it out and the person's mental fortitude can resist the destructive impulses it engenders. By the same token, an evil individual can use positive energy for healing and the like without undergoing a life-altering epiphany of some sort.
When you create an undead creature though, they have no will and no positive energy to balance out the negative/destructive influences, so you have essentially created "a mad dog on a chain" and that is an evil action. If you keep the undead under control and use them to accomplish only truly and completely good goals, then it probably averages out to neutral.
If a person tries channeling too much negative energy though, they might either start to slip towards the evil end of the alignment spectrum (i.e. a roleplay penalty) or they might take ability drain to their Con/Int/Wis as the continual influx of negative energy assaults their body, mind, and spirit.