People who are panic buying now will be all set up in their bunkers and not shop again for the next 4 weeks or so. Then everyone else who isn't and didn't think to start stockpiling a while ago can still shop.
These people will also be out of the way, not infecting or carrying the virus to others. So shops should be safer. Also note that a lot of these people are older and if they're over 70 will be made to start isolating very soon! So thank goodness they have panic bought! I know people who are 'panic-buying' for older relatives.