"Politically neutral" is a big qualifier to throw in there. You're basically asking why, ignoring his most controversial aspects, someone would find him controversial.
I'm a little unsure how anyone would even approach your question. Thiel is a deeply political person - member of the Libertarian party, for one - how does a "politically neutral" analysis of him rate that? Ignore his politics entirely? To do so is to remove the obvious reason that some consider him to be a "monster". It's certainly possible to consider libertarianism to be monstrous, if your politics aligns as such.
Even in the context of this article: he co-founded Palantir, who are a very controversial company, and will potentially assist the administration in mass deportations. Depending your political leanings, that may well make him monstrous. He co-wrote a book named "The Diversity Myth", statements in which had to apologise for in 2016. Again, those statements might make him monstrous to a person.