I read that phrase as meaning the degrees of connection feature is a way to stop users receiving unsolicited messages, something which contributes to the reverse network effects the author talks about.

Having the paid, 'message indiscriminately' feature undermines that. So if the intention is to reduce unsolicited messages to reduce spam then it doesn't work.

I think the intention actually is to reduce spam from those who don't pay for it. So yes, working as intended.

Wasn't that one of the suggestions for removing spam, by having every email sent cost something (proof of work, receipt of payment, etc?)