>This law is very clearly being selectively enforced, as lots of people have "express[ed] an opinion or belief that is supportive of" Hamas in recent days, but the police aren't knocking at their doors. (Yet.)
Every law in the UK is selectively enforced. Except maybe laws regarding speeding if they have evidence.
The laws in this country are so vague that I am certain that every adult has broken some of them.
If the Police don't like you, they just pick something vaguely relevant which you have probably broken and hassle you for it.
It's just always been the case, everywhere. The history of Law is effectively about the powerless (or rather the less-powerful) slowly carving out all circumstances in which they cannot be thrown in prison on a whim.
Well, not necessarily everywhere. In the lens of history, new countries with a new constitution don't have that problem. Over time, they create layers of new laws, then cruft when those laws make little sense to enforce, then they can crack down on the letter of that law when enforcement is socially acceptable.
Every law in the UK is selectively enforced. Except maybe laws regarding speeding if they have evidence.
The laws in this country are so vague that I am certain that every adult has broken some of them.
If the Police don't like you, they just pick something vaguely relevant which you have probably broken and hassle you for it.