SpaceX would have no part in eminent domain. Only a governmental agency can invoke that policy.
They are just seeing if offering property owners 3X what they are free market worth, would make that space available for growth and expansion. It is up to the free will of those land owners what they wish to do. If only one owner refuses the deal, perhaps no one will get the offer.
Imagine that if SpaceX cannot get the property they need by negotiation, they will pack up and find a more appropriate space to launch space vehicles. Texas has lots of open property.
Agree that eminent domain is something that a government agency does. Unfortunately, we're also seeing instances of eminent domain being used by government in order to acquire property that gets turned over to private companies for their use.
I'm thinking of instances like this (Wisconsin using eminent domain to acquire land, that goes to Foxconn for a big manufacturing facility in WI):
Masters of Our Domain: Foxconn and State Minions Seize Land
But it's just an instance, not exclusive. It seems as if we've been expanding what qualifies as a public good. Here, it's an easy argument to make - the public good is development of a space industry, cheaper access to space and the resources we'll find there. How can these 35 homeowners in Boca Chica Village stand in the way of that?
To be clear, I'm not saying anybody's going over to the dark side here, or even that they will. I consider the 3x valuation offer by SpaceX to be a completely honorable and reasonable way for them to approach this problem that doesn't get governments involved at all. They've got a particular and unique interest in a particular and unique set of property, and they're willing to bring their money to the table, to the benefit of those land owners, in order to acquire that land. This, IMHO, is precisely and exactly how it should work.
And if they want it badly enough, and the land owners don't want to move badly enough, that they need to pay 5 or 10x. Or get most of the property and have a small number of hold outs, then that's also something they'll have to deal with.
I really hope I never read an article about SpaceX removing this kind of problem by getting the local government to invoke eminent domain - that's all I'm saying.