[sonnyblarney]

"In the absence of a national ID system or local registration requirements (a la France), how do you tell the difference between a visa free entrant and an illegal resident?"

Are you asking 'how the rest of the world' does it?

Or how the UK handles non-EU visitors today that don't require visas?

Because I don't think it's a concern.

"ren't you uncomfortable with the idea that being domiciled somewhere for a couple of decades wouldn't come with voting rights?"

Not at all. Especially because 'a vote' won't hardly make a difference. What matters is the integrity of the regime in question, and Spain is 'good enough'.

If Spain wants to give local/municipal voting rights to those on long-term retirement visas, then that's fine - point being, it's the decision of the Spaniards, not some ruthless adherence to ideology such as 'freedom of movement', the harsh interpretation of which is tearing the EU apart and turning politics across the continent upside down.