but they are WITHIN their rights to demand that objectionable content not be linked

I just don't think this is true. They are within their rights to govern content that is hosted on their servers, but I really think they'd have a hard time making a legal case for banning links to content that exists elsewhere, objectionable or not. First, they'd have to spell that out in the ToS outright, and the problem with that is where would they ever draw the line? Any given link is likely to lead to a link that will eventually lead to "objectionable content." They'd have to ban links of any kind, period, and good fucking luck getting users to use a journaling service that does that.