Pretty sure the laws in the UK don't apply retroactively, but just state that new builds have to be accessible, which is hard to argue against.
> if a law helps no-one and harms plenty, it's a bad law
True, but you're picking a single example unfairly. You could make this claim about any building and accessibility - "if we have to make it accessible or get rid of it, we'll get rid of it, then no one is helped". You're missing that the law provides an overwhelming incentive for buildings to be accessible (after all, not everyone is going to pick the "fine we won't build it then" option). Without this law, far fewer buildings would be accessible, which definitely would harm wheelchair users.
> if a law helps no-one and harms plenty, it's a bad law
True, but you're picking a single example unfairly. You could make this claim about any building and accessibility - "if we have to make it accessible or get rid of it, we'll get rid of it, then no one is helped". You're missing that the law provides an overwhelming incentive for buildings to be accessible (after all, not everyone is going to pick the "fine we won't build it then" option). Without this law, far fewer buildings would be accessible, which definitely would harm wheelchair users.