I'm going to go out on a limb and say that it wasn't pain, just anger and looking to feel important. I don't doubt that he had a relative that was unhappy with the United Healthcare experience, but I seriously doubt anybody close to him didn't get medical care when he went to a $40k per year
high school and attended an ivy league school.
Also, he had the background that if he had really wanted to do something to improve the situation. Even if he thought it was too far fetched that just one person with ivy league connections and a rich family near Washington DC could meaningfully move the needle on healthcare policy, he presumably could have been much more destructive with a little bit of planning and effort. This seems like him wanting to feel important without wanting to do the hard work that's required to actually be important.
ETA: These are supposedly the properties his parents own:
www.hayfieldscc.com
So yea, looks like somebody with tons of ability that got to play life on easy mode and was bored with life.