Masks and social distancing are the only things average citizens have to protect themselves against the virus.  And masks protect those around you more than they protect you.  So, even if I'm conscientious and wear a mask, I can still be infected by someone who has the virus and refuses to wear a mask.  Just as it's against the law to endanger people's lives by driving drunk, it should be against the law to endanger people's lives by going without a mask.