I don't really see how {company-name}.sucks is any worse than {company-name}sucks.com. Do firms really go around registering every combination of bad words with their brand name, with every standard TLD? Can't imagine they do...
It appears that it is cheaper to use the .sucks TLD for activism than for preventative purposes. Given the name of the TLD, however, "activism" could be conflated with denigration. Because of this, individuals likely to be targeted by such sites are claiming extortion.
Does anyone know of any other cases in which the price of buying a domain is dependent on who the buyer is?
No, but that's because domain names have, until now, been closely held and (relatively) heavily regulated compared to other products.
There are plenty of products where the cost varies based on the purchaser's ability to pay, or their expected use. In the realm of public discourse, newspapers and other publications have long had sections where anyone could write political or other opinions for free, even while they sold ad space to commercial interests for large amounts.
Not everyone does this of course, but anecdotally, some big companies have companies that scour the web looking for negative feedback. This dept often doesn't have the power to fix anything, so they'll buy up domains and give out freebies.
There was a big uproar in the mainstream press when Taylor Swift bought up a bunch of explicit domains that could be used to deface her online presence... ICANN could just open up more explicit TLD's and she'll have to buy more and more.
Or what about companies buying up entire TLD's without intent to be a registrar -- like Google's $25 Million purchase of .app.
In short order all the "good" TLD's will be squatted on and we'll be in the same exact boat we are now with .com,.net, etc.
It's important to note that ICANN does not set the pricing for each TLD. The pricing is set by the registrar who wins the right to control that TLD.
ICANN does get revenue from each TLD registrar, but I think it's the same for each TLD. I don't think ICANN gets a direct cut of each GoDaddy sale, for example, but GoDaddy pays ICANN a fee to be able to sell domains.
At least, that's the way I recall it so I could be totally wrong.