The problem is the old system of assessing sickness and disability was full of holes - we just filled out the Income Support form and my husband would go to the local assessment centre to have a chat with a doctor about it (and I do mean a doctor not a so-called "healthcare professional"). It was, to be fair, incredibly easy under that system to get signed off as sick or disabled. And, obviously, some people took advantage of that to make false claims.
The current Work Capability Assessment obviously goes too far in the other direction, albeit having been improved a little over the last few years. My husband's first assessment under WCA was really adverserial - the woman was hostile and talking over him, I was fuming and said I'd report her to ATOS (who were the useless shower of shite doing the assessment back then). We appealed, got help from Citizens Advice Bureau (they couldn't represent us, too short notice, but were really helpful in navigating the pernicious form that needs to filled out), and on appeal got him into the work related activity group. His condition had worsened by then but the tribunal said they could only take account of what his condition was at the time of his original assessment. The tribunal was far better than expected - they asked the right questions and were polite and encouraging.
Next time around I was fully prepared and he was immediately put into the support group for ESA and, as I said earlier, they even paid for us a taxi home. It shouldn't be this way but unfortunately it is necessary to work within the system we have at the moment. I get so angry about people (like my husband) with incurable conditions that are only ever going to get worse being asked to go through this crap every 2-3 years - but it is what it is, all we can do is campaign for further change and deal with what is in front of us.