I honestly believe most go into it with good intentions, and a good portion stays that way.
But some either like the unexpected "benefits" they start receiving, or have no clue how they are being "used" by the Company and end up doing whatever the Company wants, without even realizing it.
I agree that most do go into it with good intentions. Based on what I've seen in my hub I wouldn't agree that most stay that way, though. Maybe being in a RTW state makes a difference in that.
See, that whole thing about unexpected "benefits" is something I've never experienced. I think most people can kind of tell whether or not someone is easily corrupted or not, and I'm sure higher-level management can tell more easily than most (I wouldn't be surprised if that's part of their training, to try to entice stewards that are easily corruptible). So it's a point of pride for me that management has never even TRIED to offer me "benefits" in exchange for being one of their suckasses. They already know I'll tell them to shove their "benefits" up their ass.
It's cringeworthy when, for example, a center manager insists on employees using "their" (the center manager referring to themselves) steward, and downright refusing an employee's right to select a steward of their choosing (which has been upheld in NLRB case law, and is something I point out to drivers who would rather use me, the preload steward, as their steward rather than the driver steward for their center). A proper steward is never referred to by management as "their" steward. They're either their brothers' and sisters' steward or not a steward at all.