First, Mark can run his business any way he wants to as long as he does not break the law. Groups.io is a business, not a public service or even, as far as I know, a non-profit. As many people have pointed out, taking controversial positions and stating values is no bar to success in business.
Personally, I prefer overt and plainly stated agendas. I would rather Mark state out front what he values than keep his values a secret, make tons of money off groups.io, and then quietly support whatever it is he decides to support.
With that in mind, I like the idea of a "values page" out front and obvious. As a group owner, if I have members who oppose Mark's positions, I would much rather face them openly and directly on the issue. It might decrease the size of a group, but I would rather be open.
Would that decrease groups.io's profitability? I doubt it. The market's a big tent and most folks are quite tolerant of a wide range of stated values.