Does my right to protest mean I have a constitutional right to spit Hepatitis C laden spittle on you?
Physical threats of harm are not free speech, they are terrorism. Masks are mainly effective in containing your viruses. They protect others, by capturing droplets from your coughs, sneezes and exhalation. They help promote public safety, just as do laws that ban dumping raw sewage or used motor oil. No Constitutional problem whatsoever.