I hope they don't forget that you still need visas to travel around Europe. UK is the worst offender by far for this trick.

So if they make a ring of steel based on visas, then they're making a barrier between the UK and Europe for third country nationals married to EU citizens. (The UK requires they have a visa).

I repeat that the UK cannot be part of the ring, as long as it continues to require visas for people legally resident in EU with EU residence permits.

To let them join would raise an extra barrier for those third country nationals (and the EU citizens they are married to) when travelling between mainland Europe and the UK.