I imagine it's less the tech and more that it's likely to be used for extreme political aims.

People feel other CEOs would have held back from using data collection for such drastic political means. Thiel wouldn't, and may have created the business to accomplish his political dreams.

We all try to influence society through government by voting with our feet, voice, and wallet. Thiel just happens to have a much bigger wallet, and his political agenda is pretty extreme compared to the laws that are followed today.