There's a difference between incidental and deliberate exposure. By your logic, it's ok to intentionally hit dogs because they run in front of cars every day anyway.
That said, looking at the photos intentionally is not, in my opinion, causing direct harm, nor is it driving demand. To say it is would be like arguing that pictures of dead bodies fuel demand for murder. It already happened, and not looking doesn't change it.
From my perspective, it's simply immoral. If it violates your morality, then don't look. If it doesn't, then check them out.
By the way, the desire for privacy and the desire to see other people's secrets are not mutually exclusive. It's our desire to see the things that other people want to hide that underscores the importance and value of privacy. It's nobody else's business what I do in my own home, or what photos I took on my phone, as long as I'm not violating the law.
Further, there's a difference between my neighbor violating my privacy out of curiosity and the government peeking at my journal to decide whether or not I belong on a secret watchlist. My neighbor cannot legally take away my rights and freedoms; the government can. My neighbor can be prosecuted; the government (generally) cannot. That's why evidence that's been collected or presented in violation of evidentiary rules is, or is supposed to be, excluded as fruit of the poisonous tree.
One more side note: If these photos happened to show illegal activity, the government *would* be able to use them as evidence, as they were obtained incidentally.