Edit: Here’s a link to what is most likely the real manifesto: https://www.kenklippenstein.com/p/luigis-manifesto
Ken Klippenstein is a very reliable journalist and this version of the manifesto contains the snippets that have been released by law enforcement. Also, considering the thing was hand-written, that very long version involving his mom is dubious. (And there’s not any good evidence that his mom is in anything besides decent/good health)
I have only ever heard opposition from doctors (or medical students) that were right wing/conservative to begin with. Most of the doctors I've worked with (especially those in emergency medicine and family medicine) are very much in favor of universal healthcare.