If you don't have time to consider your own safety, you don't belong in public.Some people don't have time to fumble with masks, putting them on and off in a sanitary way, or it causes more contamination by contact or placing the mask on surfaces touched by hands.
It defeats the purpose.
Medical professionals keep their hazmat gear or PPE on without touching, and remove to replace them per shift. This reduces contamination by manual contact.
Wearing a dirty mask is what defeats the purpose. Which is why I call BS on your claim concerning medical professionals. You claim that they continue to wear contaminated PPE while treating persons who are not contaminated, thus making them to spreaders.
For once, think about it.