I like to run that evil has a corrupting influence, good is similar but people tend to speak of goodness as 'uplifting' etc, but in the more general formulation that using the powers and tools provided by [alignment source] has a small tug effect on those using it, if only that access to such things generally comes from interacting with such entities or invoking such powers tends to attract such forces.
That could be cool, but you always have to deal with the logical conclusion, which is the hard pill for most (even those advocating these things) people to swallow. The logical conclusion being that if it does have a pull on your alignment, even a small one, then ultimate it means you can just buy your alignment.
It's just a matter of how many castings does it take. 10? 25? 50? 100? When you realize that it means that crafting a wand of protection from evil means you are bottling 50 acts of good and putting it on sale for 750 gp. And most people when presented with this fall back to "but evil is more influential". Then it becomes "why?", and we spiral again.
Further, if it makes you more X, but you still have free will (which alignment doesn't remove) it basically poops all over the point of alignment and makes it both cheap and shallow. It doesn't really matter if you're evil, because you might have gotten there being a pretty average person overall, you just happened to be a bloodline sorcerer who used their bloodline magic regularly.
You basically end up in a world where alignment no longer has a lot of meaning in terms of who a person is, it's mostly about which element he picked. It's down to fire mage vs frost mage. There's not really any reason for good to be against evil so much as you're against some of the things that evil does that are actually harmful (like murdering) but you're not really against all evil (because Mordrin's Tireless Oxen service "60% off this weekend" isn't exactly worthy of your time).
One needs to address this in an in-universe way, come up with some good mechanics, and make it work in a sense that doesn't seem dumb at the end. The closest I've seen to these is corruption mechanics like Taint or Sanity.