> This makes me afraid of “You can take time off as long as the work is
> done.” Am I wrong…is unlimited PTO generally beneficial to employees?

You're not entirely wrong. 

In states like California, companies do select such a policy for themselves because they don't want employees to accumulate PTO, nor do they want to pay out vacation time whenever an employee quits, or gets fired, or gets laid off. And yes, having such a policy does have a chilling effect on employees taking the PTO they're entitled to. 

But at the same time, if you're applying to tech companies in California, it would be really foolish to avoid all companies that have such a policy because it's very common, plus for some companies, it's not always a negative for the employee. 

If you want to see how the policy works in practice, ask your future colleagues (at your level) during the interview. 

"How does this "unlimited PTO" policy translate in practice? During your first year, how many vacation days did you actually take?" 

With that said, I understand if you don't want to ask too many questions related to PTO during the interview itself. 

So definitely, talk to your friends/acquaintances, have informal coffee chats with current/former employees, use sites like Glassdoor, Blind, LinkedIn, and use Google (if the company is large enough). There is a lot of bad information you can uncover that way. 

But definitely do not blacklist all employers that have such a policy. If you're applying to jobs in California, doing so would be sabotaging your own job search before it even gets started.