I'm not sure I share that confidence. Even if you're right, the time, expense, and emotional pain of merely being sued is substantial, and it all happens before the jury even enters the picture.
There are plenty of people who will be happy to sue. They will sue. They will sue over an unavoidable outcome. They will sue over the triage decision that denied treatment to their dead family member. They will sue if their dead family member didn't get a particular treatment because supplies were short or unavailable. They will sue because they are entitled, obnoxious, selfish people ... or perhaps just because they in pain, and naive and genuinely believe that unlimited healthcare on demand at no cost under all circumstances is a human right, and a physician that doesn't or can't do that, is either criminally negligent or a profiteering war criminal.
If the US public hadn't consistently been waging a campaign of denigration and marginalization of physician "providers" for the entirety of my ~20 year career, I'd have a little more faith in that jury. So I don't think it's unreasonable for people to be concerned about the medicolegal risk associated with practicing medicine outside of areas for which they are trained, credentialed, and insured.
If our government would take a moment, while bailing out airlines and cruise ships (!), and explicitly augment Good Samaritan laws in order to make physicians immune to lawsuits stemming from practicing outside their area of expertise when caring for COVID-19 patients, that'd be nice. But they won't - see the line above about two+ decades of denigration and marginalization. They hate us because, unlike nurses, we haven't been waging a self-aggrandizing propaganda public relations campaign about how compassionately selflessly great we are while punching a clock for shift work.
All that said - despite the validity of these concerns and these risks, I would absolutely think less of a physician who refused to work during a crisis like this. I would remember it. It would influence any reference or hiring decision I was later asked to give or make. This is more than just a job. We have a duty to care for the sick and injured, and to be of service to our country in its time and need. Yes, they're free stay home if the billing slows. I'm free to remember their absence and later act on this new knowledge of their character.