So long as they share the revenue with me, I'm okay with it. I have for years wanted an inbox where I could charge people to email me.
If there were a hard cost per recipient, the ROI of email campaigns would change significantly. This change would be positive for users. The question is whether or not senders would bear the burden, or if they would flow to "less legitimate" means of reaching recipients on Facebook. It may be that senders would more willingly accept lower actual reach rather than pay the additional cost.
Seems fairer, no?