I agree with you that the comments above aren’t very persuasive. For example, the ones about billionaires are clearly ad hominem. But if that’s so clearly the case, why bothering deleting them (especially since you’ve re-posted them here)? You can just say they’re ad hominem, as other posters no doubt would. Ditto for the other ones: I don’t know anyone who would take them seriously. All deleting them will do is feed the theory that progressives can’t tolerate freedom of expression.
Finally, I don’t agree with the argument ‘we’re not limiting the freedom of speech in general by deleting some comments.’ Of course there will remain plenty of places where people can say what they like. But if you delete comments, there will be one less place, and I think a liberal outlet like this should be expanding the space of free expression, not contracting it. Besides, you’ll make it harder for your readers to see the full range of views that’s out there.