|"Gee, I guess because of eminent domain, Ike's plan to build an interstate highway system couldn't be done."|
It's not the same thing, and you know it.
You clearly don't understand TX landowners. They don't want this. The border is the Rio Grande, but because of the flood plain, the wall has to be built about a mile or so back. So not only do they lose access to the part of their land the feds don't take, but it's still American land. So you've got this wall a mile back from the border, and immigrants can just swim or wade across the river and step on American land - which by American and international law allows them to ask for asylum. What have you accomplished?
"what difference does it make if it's concrete, steel, fiberglass or even plastic?"
The difference is that his campaign promise was that it would be a "big beautiful wall", solid concrete, thirty feet high. That's what he promised you he would do in an attempt to get your vote. And now the Trump cultists are saying the same thing as you're saying - what he said doesn't matter, just put up a barrier wall. The reality is that that barrier wall will never be built during his presidency because of legal issues. He says that construction has already started - it hasn't. That's just another one of his 10,000 documented other lies that are just intended to fool the low-information members of his base. What HAS happened are repairs to existing barriers previously authorized by Congress - not a single mile of the promised new wall has been built.
You should know this - you're clearly not a stupid person. This whole wall thing is nothing more than reality TV/political theater - and it simply will not happen because of the legal issues involved. Eminent domain claims on the border from the GW Bush administration are STILL being litigated 10 years later. What legal magic do you think Trump can perform to make a citizen's Constitutional right to their property go away without the court's approval?