abgd, could you possibly, to avoid misunderstanding, reword your statement: that says, "If you crash a glider on land, it's common to survive fairly serious injuries...." o dear. seems to imply it's common to have serious injuries!"
How about, "when doing a field landing in a glider, it is rare to either damange the glider or yourself!"
BUT. I will share with you a famous water landing made in December, in Wales. Gets dark pretty quick in December, and the glider had not returned from soaring the Black Mountains. All at the club were concerned, sent out the tow plane to search, no luck. Thinking perhaps there has been a fatality....
Fairly dark, about 9 or 10 that evening, the phone rang. The pilot said I'm OK, but there is probably damage to the glider.....I'm at a farmhouse, and the farmer will give me a lift back to the club.
Next day, they hitched up the K18 trailer to a Landrover, and set out off over the hills, and on the other side, there was the Reservoir, and there, undulating in the water, was the glider......
The pilot said later that he couldn't get back over the mountain, so had a choice between a tree landing or a water landing, so chose the reservoir. Then he had a choice betwen the shallow end, or the deep end, so he landed at the shallow end, unlatching his canopy as he touched down. However, the canopy burst open, the water flooded in and SANK the glider, and the pilot was underwater, held down by his straps! which he did manage to undo, and also his parachute straps, and waded to the shore, and through the snow to the only light he could find, the farmhouse.
They managed to fish out the glider, floppy wings and all (the glue had melted overnight) and take it back to the club, and a year or so later it was rebuilt.
The pilot (this was his third unfortunate landing, he had written off two other club gliders elsewhere) then bought his own private glider, which never came to grief. The pilot did well to enjoy hia exciting life, for he passed away a few years later from natural causes.....
So to return to the original question: crowded beach? same ethical problem, you wouldn't land in a school playground either. So ditch in the water; if it is too cold to survive the ditching, there won't be a lot of people in the water anyhow, so close to shore should improve your chances.