It's irrelevant what you plan to spend the revenue on. My hobbies cost money as well, but I don't subsidize them with ads. I pay for them with my own money.
If you want to run a blog as a hobby, great. Spend your own money to buy hosting and be done with it. If you want to generate revenue off your hobby, that's fine as well, but know that it's not purely a "hobby" anymore. Even if the amounts are small or you're not profitable, it doesn't matter.
EDIT: Sibling comment may be more accurate. If you show non-profitness, (I'm speaking abstractly, not in relation to linked court decision), that would be enough to sever the link between the otherwise infringing links and your revenue.
