Google ‘rear speeding’ and it comes uo with a link to this thread (good job on the page rank webmasters) and a few things about traffic accidents – i think you chaps just have dirty minds.
Maybe I got the knee thing wrong, I thought singlespeeding was hurting my knees – when going uo a steep rocky climb have to keep the weight back so the rear keeps traction so not standing up on pedals and then pulling up on handlebars and putting a lot of force through the leg in order to climb at 40rpm.
Worst of both worlds – I dont see it that way as it is cobbling together a useable bike from a bunch of spare parts which was the original ethos of singlespeeding whilst having a bike that is a bit more useable on a variety of slope & terrian.
I think another reason I like rearspeeding is a majority of drivechain woes come from the front mech, rubbing/rattling, chainsuck, much faff getting it aligned & adjusted right. So rearspeeding goes quite a way to achieving the simplicity of singlespeeding.