I know ETIAS doesn't affect intra EU travel. My point was we have both experienced the benefits of unencumbered travel (within the EU), why then support raising barriers to other nations?

Security and illegal migration seem dubious reasons to introduce (not) visas for the US. Is there a problem with illegal immigrants from the US? Terrorists?

So then we're just left with tit for tat politics. I for one would like my politicians to be more mature (ha!). This is how trade wars, and worse start. I personally would like to lead by example, be the better man, and be a good neighbour. If others don't wish to, that's their problem.

ETIAS applies to all travelers to the EU from all visa-free countries. So it isn't a "punishment" for US specifically. It is a generic change to how EU handles visa-free travel. One might argue that e-visas (which the ETIAS is) are bad for free movement of people in general. In my opinion if ETIAS (and similar systems in other countries) make traditional visas move toward obsolescence by allowing traditional-visa-free travel, it is a good stepping stone to "more free" movement.

True free movement would then be reciprocal, i.e. EU-US travel would not require either ESTA or ETIAS. Basically that would mean US would be part of Schengen Area or a new similar structure.

The discord about US requiring visas from 5 EU countries is a separate issue that might bring other actual "tit for tat" measures if not resolved.

Visas don't have to apply to all nations. The same would seem to be true of ETIAS. So the principle still stands. Why increase barriers to those wanting to travel to the the EU? Yes the stated reasons (illegal immigration, security) will apply to many countries, but that shouldn't be the default. The default should be unencumbered travel, unless there's been shown to be a good reason why that shouldn't be the case.

The US’ ESTA system exempts Canadians. So such systems are definitely capable of picking and choosing.