I think maybe this is a feature rather than a bug.

I know at least a couple of subreddits for specific 'true crime' cases which split into one for people who believed the suspect was guilty and one where everyone believed they were innocent.

The thing is, the split fora were actually much better than pre split. When both sets of people were together every topic degenerated rapidly in exactly the same way:

    meticulous_postrr: I just reread the transcript of Fred's sixth interview and noticed that he mentioned seeing a purple t-shirt in the woods. Could this be the shirt that Ahab was wearing at the road house, which looks blue in the security footage? 
    middled_aged_loner: Nice try, but unless you can explain the severed foot in the ashtray, the blue shirt is irrelevant here. 
    AhabDidIt: Still trying to shill the 'only two feet' theory, m_a_l? What about what Edgar saw?

    curious_n00b: Hi, I love the podcast but I'm not sure about one thing: is the Sylvia mentioned in Dushane's diary the same Sylvia who knew Edgar from volleyball camp? 
    AhabDidIt: welcome curious. Good question, but you're wasting your time with the diary. The July entries were written in August, by April. See my previous threads /r/TheScarletFred/Ahabs_lies /r/TheScarletFred/Ahabs_lies_2 and /r/TheScarletFred/the_diary_evidence_reexamined
    middled_aged_loner: So in your opinion ADI, April apparently knew that Dushane had seen Vanessa on the rollercoaster but didn't mention it to the police on the 1st October? This completely fails to stack up. What about Vanessa's unfinished ice tea? WHAT ABOUT THE SEVERED FOOT?

The split subreddits have better information, better curation and better flow. People who are otherwise in agreement debate precise points carefully and in detail. Both are available on the same internet so anyone who wants to can read both and make up their own mind.

I know we're all supposed to be worried about echo chambers, but sometimes an echo chamber is somewhere a specific conversation can take place which couldn't elsewhere.