I'm sure there are many people who think this is ok, because it's not the government doing this, but a "private company". Who needs a totalitarian dictatorship when plain old capitalism works as well if not better?
What would be totalitarian is forcing a company like MailChimp to expose itself unwillingly to the ethical and legal liabilities associated with this field.
In other words - there's a high barrier to entry and you can't provide the service at all if you don't have a certain amount of volume to make a certain amount of profit to cover operating costs. Targeting a niche will not provide that volume.
Anyone with an email server can try, but given the nature of this particular community it is more likely that this competitor would soon find their email delivery rates hitting 0%.
Seems pretty rational to me...
As an aside, someone could easily set up an ICO to fund a competing business to take a big chunk of Mailchimp's user base -- assuming they weren't fraudsters, of course.
That's been well known since at least 1848...