For many of the supposedly "opinion-based" questions, reasonable people will at least agree on the relevant trade-offs, even if they come to different conclusions overall. Thus, when a question asks about "pros and cons of technology X", expert insight into the trade-offs involved could be really useful to help evaluate your own specific situation. But that kind of more nuanced question doesn't really fit the simple "one correct answer" model that Stack Overflow seems to be going for and is thus very likely to be closed. IMHO, there should be a distinction between "it depends on the circumstances, and here's why" and "purely opinion based", and Stack Overflow would be more useful for me personally if the former were allowed.

Edit: Just to check if moderation policies have changed since I last looked, I did a quick search for questions containing the phrase "pros and cons". As unfortunately expected, practically all of the questions are closed: https://stackoverflow.com/search?q=pros+and+cons