Sometimes company leaders have severe problems with ethics. As mentioned in other comments, even YC has had companies that have bundled adware/malware with software, practiced dark patterns, hidden news of security breaches, etc. I tend to see YC as being more "evolved" than other VC's, but I also think that these problems are more ingrained into the human condition. YC could consider making funding contingent on all…
I wonder if I am too cynical, but at the root of it the main purpose of building a company is to make money. You might genuinely want to change the world but that is emotionally secondary to gaining wealth. To be a successful entrepreneur, it helps to be ambitious and generally this is a trait that is unlikely (though not unheard of) to be paired with a significant degree of concern for others.
Most companies, and many large tech companies have shady practices, usually in the form of misleading advertising.