Maybe you think it should be. I personally think it is protected if the people being photographed consent to the publication, and a violation of privacy if they don't. (Privacy and free speech are both human rights, they don't conflict.)
We can have that conversation, though, if you think that privacy isn't a human right.
But the people who are upset about this don't seem to be talking about that. They don't talk in terms of human rights, they paint Theil as a bad guy and try to paint him as being opposed to freedom of speech.
But can you cite a single quote from Theil that has him on the record as opposing freedom of speech?
We should not accept this kind of smear as if it were legitimate argument. It doesn't appeal to reason or argument it is characterization.
And it is eating all discourse. For every time I see an actual argument against a policy of Trumps (notice how they dragged him into it?) I see at least 150 claims that he is a racist. Not quoting him saying something racist, just a smear. And that ratio is probably higher, because to be honest I haven't seen any coverage of Trump in the last 6 months that makes a good reasoned argument against one of his positions.
It's not like it's hard.
Here's one of Trumps positions I disagree with: We should have open borders.
Closed borders is really saying that a company can't hire who they want to hire- that you can't hire the best and the brightest in the world and bring them to america, one of the things that made america great in the past. We shouldn't nationalize talent we should have a free market in it and let anyone who has a job offer (at least, there are legitimate arguments for an even lower bar) come to the country.
There. That's an actual argument against a Trump position.
A similar argument could be made against Theil. They almost make one against Zuckerberg (but in the end they resort to characterization of Facebook as a "walled garden", which by that definition means The Guardian is a walled garden because the editors control what is published on their site.)
Discourse is dying. Don't let it.