"Wall Street is like any other business. Don't over-glorify working for Google and not Goldman: tech companies are in it for money too; so are startups. At least on Wall Street people tell you they're doing it for the money. It's easier to detach that way and remember that what you're doing is just a job."
You may try to justify what you do that way, but it's just cognitive dissonance. "Wall street people" tend to make money in rent seeking ways, destroying or merely transferring real value. At least at Google you could be creating value, growing the economy in sustainable ways, and increasing real GDP.