I don't perceive poison use to be especially evil in any given context.
Poisons hurt beings excessively? So do : swords and maces (these kinds of jolly 'murder-aid' tools will - on a regular basis - produce diabolically slow and agonizing deaths), burning alive (e.g. courtesy of a righteous CG wizard's Fireball spell), being partially eaten while still alive (e.g. by a NG Druid using Wild Shape), and so on. D&D (in the core rules) is rather bloodless, but - to me - that hardly seems the right 'colouring' for a system that is inherently extremely violent, and so for those who want a little pain with their gore...er, no, let me rephrase that...um, for those who enjoy some - token of course!

- realism in with their fantasy gaming, adjustments must be made accordingly (or supplements purchased, alternatively). Anyway......
In the Book of Exalted Deeds, there are feats and Prestige Classes that specifically enhance and employ Sneak Attacks, respectively - so there go the 'dishonourable' and 'stealthy' versions of "Poison Use Is Evil", really.
As has already been stated a few times, various good-aligned beings utilise venom freely with (apparently) no pangs of guilt.
All in all, what will those bloody paladins think of next eh? First it's the poisons, next it'll be your daggers, mark my words. You'll be fighting with a good knife in a fair and honest duel someday, and mr. paladin will just step right up and rip your head off barehanded for the dishonour of using a weapon with 'less than lawful visibility'.
And that'll be the beginning of the end, truly.