I have a neighbor who used to work as a landscaper. The money was decent (in SF); his specialty was masonry. Then a couple of years ago, he decided to drop out. Claimed he had MS and started getting SSDI checks of about $2K/month (I think). After he dropped out, I've seen him lift 100lb stones; frequently, he'll drive down to Arizona for fishing trips with buddies; and recently, he drove cross-country to Georgia for…
Also, to take a very personal example, I've also got a neurological condition (not MS) that is fairly episodic. I'm fortunate that I'm have got a desk job as a software developer and so I haven't had to seek disability (despite being told by my physician he'd support an application). If I had to work going physical labor, I wouldn't have a choice but to apply for disability, since when my condition flares up I'm fairly immobile. Even walking short distances is difficult. There's simply no way I could hold down a 5 day/week physical labor job.
That said, when things are going well, I can be fairly active. Today I was out working on my deck. I take my kids to the zoo and walk around the entire park. If I had had to take disability, would people say the same things of me?