Recently, *not constructive* has been changed to *primarily opinion based*. Some questions simply don't have a strictly evidence- or fact-based answer and the best answer is the opinion of majority. Or sometimes it's the opinion of some authority that makes the perfect answer. 

There are many great questions that helped me understand game development on this site and a lot of them are opinion based, with *I think...* answers.

**Why are primarily based questions not welcome on this site?** Apart from closing them is there anything else we can do to prevent debate, arguments, polling, or extended discussion? Is it possible to deal with primarily opinion based question in other way?

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Closed opinion based question that influenced me the most and the wisdom from accepted answer is repeated many times in other questions/chat:

* [What things should an indie game developer never do?](https://gamedev.stackexchange.com/q/765/30949)

Great question that I consider opinion based and was not closed:

* [How to prevent the "Too awesome to use" syndrome](https://gamedev.stackexchange.com/q/55558/30949)

Question that I consider opinion based, but is nevertheless interesting (still very active):

* [How are boss battles important?](https://gamedev.stackexchange.com/q/58819/30949)