I think it's absurd to have US immigration policy enforcement on Irish soil (I suppose there's a diplomatic carve-out for whether the post-immigration area is "US soil" or whatever, but still).
As said policies become increasingly inhumane I think Ireland should consider removing this arrangement. But you are right, Dublin Airport themselves do benefit since it makes them more attractive, especially as a transfer airport for people going to the US from Europe.
Is it “absurd”? If you’re going to be rejected access to a country, wouldn’t it be better before you get on the plane? Seems the opposite of absurd, it seems preferable.
UK based travellers travelling to Europe via either the Eurostar or Le Shuttle go through French immigration on UK soil before departing, this facilitates easy exit in France. Makes perfect sense to me, as a UK national I don't see this as impinging on UK Sovereignty.
I can't even imagine a situatuion where this is not preferable. For example, if the US immigration check happens in Ireland, they can't detain you or mess with you in ways in which Ireland doesn't approve of, which they could if you were on US soil.
If anything, it seems to me that the USA agreeing to perform immigration checks in Ireland and accept them when you reach the USA is a(n extremely mild) limitation to US sovereignty, not to Irish sovereignty.