I think that's a really important concern. At 80,000 Hours when we encourage people to earn to give we ensure they're embedded in the effective altruism community, take things like the Giving What We Can Pledge and so on - mechanisms by which to ensure that our future selves don't fail to live up to our ideals.
It's also worth bearing in mind that the rate of people becoming disillusioned when they do direct work in charities also (anecdotally seems to me) to be very high. Reason is that it's often very hard, often you don't feel like you're having much of an impact. Whereas if you enjoy working in the lucrative career you're in, the 'sacrifice' of donating even 50% isn't really that great, so it's potentially easier to continue in that path. I'm genuinely really unsure which has the greater dropout rate: earning to give, or direct charity work. If I had to bet I'd say it was direct charity work.
It's also worth bearing in mind that the rate of people becoming disillusioned when they do direct work in charities also (anecdotally seems to me) to be very high. Reason is that it's often very hard, often you don't feel like you're having much of an impact. Whereas if you enjoy working in the lucrative career you're in, the 'sacrifice' of donating even 50% isn't really that great, so it's potentially easier to continue in that path. I'm genuinely really unsure which has the greater dropout rate: earning to give, or direct charity work. If I had to bet I'd say it was direct charity work.