I have some big personal opinion questions I want to discuss, that would fit perfectly into this site if they weren't so open ended.
So does anybody know where I can ask them?
One possibility is to visit the Factory Floor, our main chat room. Depending on your timezone the activity there will vary, but in the chat we welcome open-ended opinion-based discussions about worldbuilding. This is also the perfect place for a bit of brainstorming if you are thinking about an idea, but don't have a draft yet.
If you have a draft you could also try the Sandbox where others help you to fine-tune it to the main site. If the question really is open-ended and opinion-based that won't help, but in case you are ever not sure if there isn't a way to make something on-topic it's worth it to drop a draft into the Sandbox.
If the chat is not useful to you and the question just isn't a good fit for the site then you have to try different sites. There are many good questions that just don't really fit the StackExchange Q&A style. Personally I don't use other worldbuilding related forums, but I've heard that there is a subreddit that might be helpful for you.