[sigwinch28]

> What's the risk here?

A monopolistic stock exchange could, off the top of my head: increase fees, engage in rentseeking behaviour, impose unfair rules, discriminate (against companies and traders) or reduce the quality of service.

Listing on different (or multiple) exchanges ensures that they engage in proper competition.

> compared to the actual extractions you are subjected to in the UK

An apt example of why it's healthy to have competition. A working professional or business could relocate to a country where less of their wealth is taken from them.

[FredPret]

But your parent comment's point is that the harm from lack of competition among exchanges is a possible future thing, while the harm from being domiciled in a business-unfriendly jurisdiction is far greater and happens right now.