TSA's argument (and it has some merit) would be that there are germs everywhere. Pax with known immune system weaknesses should already be taking extra precautions every where they go.

For those pax with normal immune systems, well....we've gone over a decade without an outbreak of something at the checkpoint, so clearly that proves that the risk is low to non-existent.

I put 'checkpoint socks' on before the TDC and remove them after the checkpoint because I don't want to put filthy feet back into my shoes. I'm less worried about the general filth than I am about cross-contaminated swabs (and what that can lead to) and hands running through my hair (glove change, please). I do not want to pick up something disgusting like head lice. I'm amazed when I see a TSO running hands through pax hair and then touching his/her own hair without changing gloves. Not a risk I would take.