Tourism gives you money, which is dependant on how large your population is compared to that of the rest of the galaxy (I think? Anyway, it's based on the size of your empire). That would more likely than not be more than enough to make up for the -1 or -2 bc that each colony is losing. If you look at the domestic tab, in the spot where it shows your net income, it should have two columns, one that displays your income, and one that displays your expenditures.
