I think you will find after some more experimentation that, if you type in www.reddit.com, the HTTP code you get back is actually 302, a redirect to HTTPS. Which is correct and corresponds with best practices for HTTPS redirects. Typing in https://www.reddit.com instead will yield the correct result. It doesn't help that the route checker deems those redirects as errors, too, and so colors the cell's background red, so I agree in so far as one of two things could happen to remedy this:
The background color should be yellow to indicate a redirect which doesn't have to be a block. But that tool is actually there to tell you "yep, works" or "nope, not from here" at a glance. Yellow as in "meh, maybe, check yourself" is beyond unhelpful.
If a web server returns a 301 or 302, follow the Location header once to cater to the common case of a HTTPS redirect and print the result for that new URL. But this could produce false positive results: If a website viewed from the server returns a 302 to a webpage basically saying "sorry, you've been blocked", that webpage will of course have a green 200 return code.
What a sweet dream.
Check out OneDrive/Outlook, Netflix, Hulu, BBC iPlayer, etc. and maybe all those sites sitting behind a Sucuri WAF.
What you could do is to keep track of the Blocked websites warning forum and update your list with every new thread and post. It'd be a help, but would demand work from you alone, continuously even. But if effective, such as thread could be pinned in this forum for visibility and be a boon for the community, I'm sure.