Generally, even the most staunch libertarians are okay with such things because the payments and relationships are voluntary, issues like monopoly and free will notwithstanding.
But Twitter, FaceBook and even Google demand a form of somewhat involuntarily payment: time and attention. For some people, mainly the lucrative few who subsidize everyone else, time is much more scarce than money. These virtual "time-pennies" are sliced away in such negligible chunks that lead us to think we're not getting ripped off, but it's siphoning away an economic scarcity nonetheless, and everyone who participates in social media or any ad-supported services (which is asymptotically approaching everyone) pays the tax.
That's what Twitter's new rules really come down to: they couldn't give two figs about ensuring a consistent experience. It's an unsubtle smokescreen for "don't you dare interfere with our ads; that's our bread and butter you're f&*king with." It wouldn't surprise me if after locking down the client apps, they begin an aggressive cat-and-mouse game with ad-block plugins.
Is there anything wrong with any of this? Not inherently. But I'd much rather pay into a semi-socialist freemium service than one where my precious attention is sold to the highest bidder. (Dear App.net: go free-for-most with a paid tier, and you just might take over the world.)