Beginners Polo

That said, there seems to be a divide among the people I talk to about this question. A few people have been very vocal about less-strong players checking out any game they want, while others I've asked have discouraged it.

Really? Who has been vocal about this? Other people at beginners?
You should feel free to go to any regular throw in you want. But as you then say yourself:

I fully understand people's reservations about encouraging beginners or near-beginners on faster courts. Just about every other sport has tiers, so that people are matched as far as experience goes.

You'll get more out of playing with people roughly your own ability, especially when starting off.

You wouldnt walk into a Premier League game if you were learning how to play football, or suddenly compete with Chris Hoy if it was your first time on the track.
Well, you might, but you'll be out of your depth a bit, probably wont learn too much, or have the space to develop your own skills, becoming disheartened in the process.

A beginner showed up at Downs on a Sunday morning six weeks or so ago. Cosmic (arguably the best team in Britain) were playing their usual Sunday games there. I cant remember who else was there for throw ins, but (as always) when playing against, or even with them, it was incredibly tough to keep up and get involved in the game.
I dont think the new guy touched the ball once in his two or three games where he played, unless we rolled it gently to him at the reset - and I dont think he's ever come back since. I told him to go to Peckham - but I didnt mean it in any aggressive, highly vocal way, it was more just to get him used to it, and to enjoy the game, so he'd feel like his skills were improving, and he'd come back again.