You may think Mr. X is rude, or selfish, or greedy, but so what?
How would you tell nice people and evil people apart if it wasn't for their greed or selfishness ? We're not talking of keeping a lawnmower to use it at the moment, we're talking of sitting on it by principle. Nothing is lost through a visual quote on a forum, a catalogue, a clumsy fan-fiction, etc. It's not because Tintin's icon is "busy being used elsewhere at that time" that Moulinsart threatens innocent usages of that cultural reference.
I don't like the analogy much (because physical objects and virtual images aren't the same), but if some people "share their eraser" and others not, it does indeed mean some are better people than others - or at least that's how I've been endoctrinated in school. I doubt Tintin barking "NAW, it is MINE" would have been judged as a very noble exemple to print, even by the current "tintin spirit" watchdogs. Going "what, you touched my eraser while I wasn't here, this will cost you 6000$" may be a legal right, it still belongs more to a Rastapopoulos confession than to a Tintin deed. What I'm getting at is that such differences of attitude are exactly what defines the position of people on the "good/evil" continuum. And by annoying and suing innocent people (that is, people making decent usage of the tintin image), Moulinsart does add its share of ugliness to the planet.
It's not a matter of "rights". Laws allow (and at times support) quite a bit of regular everyday evil - and it's people's "right" to be evil to some extend (vote for the fascist party, insult beggars, steal someone's place in a row, belittle fragilized people, exploit workers, select friends on the colour of their skin, whatever). It doesn't mean people who do are as good as those who don't. A lot of choices have no moral significance (like, what consentant people do in bed, or what music they hear), other choices contribute to make the world more difficult, hostile or grey. The history of Tintin copyright is full of the latter, moreso than any other character copyright.
You can check for other comics forums, also supervized by author widows, and find colorful "visual quotes" illustrating posts points, or even little "draw the next page" fanfiction games. Imagine Moulinsart's reaction if I was to spontaneously illustrate a tintin quote with a scanned image (without having written them a letter and paid them 500 Euros per post), or if a multi-users fanfiction was created here. I can already hear their lawyer's hands being rubbed, with a gleeful "yay, that'll make us $14000 per participant, sue sue". They're legally entitled to that. But it does make them antipathic people in my book (greed, selfishness, and not-lending-your-lawnmower does). "They have their reasons", yes. Precisely.
Or maybe I've just read too much Tintin.