Ok, great, so what specifically is the policy you feel that Substack should put in place? I'm inviting you to take a stab at defining at least the rough draft of one. If you can't - if you can't go any further than nebulous terms - then that's just reinforcing my above points and the more general point that it's more or less impossible to do censorship well.
It depends entirely on your objective. If your goal is to run a site that is your own little corner of the internet where the only views expressed must conform to your precise world view, then that is totally fine and can be very, very effective and (relatively) easy to implement. The content policies for most private companies are basically this, as are many newspapers. Perhaps the most key point is that on those sites, the content is theirs.
It all falls apart once you move to user-generated/-contributed content. So, for example, if you want to create a place for the best modern thinkers to come and debate how society should address the modern challenges of our time, how much do you moderate that? Your willingness to interfere with the discussion is directly at odds with your goal of becoming "the" place for this sort of thing. Authors are well aware that the audience/following they build is at least somewhat tied to the platform they use to build it, and many people - possibly some of the people you really want - are going to balk at a policy of "we can take down any post at any time for any reason". It doesn't make your policy right or wrong, it's just at odds with your cool business idea, that's all.