With respect - and I am physically disabled and opposed to the proposals - but your comment implies that physically disabled are somehow more genuine than others. For starters, I am simply not going to pretend that there aren't people faking it, although they are few - but I have come across people faking physical disability, so there are some. And equally some physical disability can regress - again, it may not be common but that doesn't mean it doesn't happen. The odds of someone with severe mental illness being able to "pull their socks up" and cure their illness is about the same as someone with a physical illness being able to.
We do no favours to anyone by standing divided. I am all for rooting out any fakers. I am also all for supporting people with disabilities to get into work if they are able to do so, not to help out the poor taxpayers (I am one of them - disabled doesn't mean incapable) but because being in work is better for people. But no disabled person should be "punished" for not being able to work, full stop. If we have too many people with disabilities out of work, then we need to fix a whole host of things including employers, training, accessibility, transport, educatioin and the health service.