It is like that in parts of my company. If I need something, I wander over to the desk of the person who works on it, who I know, and I say, how about it, and he says, cool (or vice versa).

The other group write up huge requirements documents, set up Sharepoint sites and wikis, raise tickets and Jiras, you name it, but they never talk to each other and so they get nothing done...

That's the thing, Scrum basically assumes that all software teams are so dysfunctional that they won't talk to each other unless and until everyone is watching.

Scrum! It teaches bad teams good habits!

Nothing in scrum stops you talking to anyone at any time. The stand-up makes sure that you have to say a few words to the whole team and other interested parties, daily.

I like to read criticisms of scrum, when they're not straw-man ones.

How was the parent a straw-man? He suggested that teams that can't talk to each other without the prodding of Scrum are dysfunctional (which I happen to agree with). That's not even necessarily a criticism of Scrum, it just points out that Scrum can be good for teams that, as you say, have bad habits.

I didn't mean it as a straw-man criticism, just an observation that scrum is very rigid and prescriptive; it's all about the what and the how instead the why.

I'm a big believer in trying to persuade people to keep feedback loops short, make teams small and cross-functional, and to design/code/test/ship in the smallest increments possible. At this point, calling an approach agile/scrum/xp carries a lot of baggage.

If people don't get the why (e.g. the team isn't small and cross-functional, and people aren't working on tiny increments) it kind of doesn't matter if you get everyone in the room at the same time every day.