They aren't holding intellectual property hostage. And by the way, when is personal gain evil? Do you go to work each day primarily to benefit other people, rather than yourself:?
They are providing added value, they registered a domain that someone else didn't think of.
The problem here is, that you regret not registering it, and so you, rather than accepting blame for your own failure, are blaming the person who was smarter or faster than you.
Back in the 1990s, I looked up USWeb.com. I almost registered it, but was on the fence, then went back three days later to register it and found that it had been taken the day after I thought of it-- and that company became a big company eventually before the bust.
Were they holding my intellectual property hostage? No.
Where does this sense of entitlement come from? IT reminds me of people who build a house in a neighborhood and then complain because a walmart gets built nearby... as if they think they somehow have property rights in the land that walmart bought. LOL.