Here's the basic argument:

1) Lockdowns are 1000x more intrusive/draconian than foreign travel bans - one sets the border at the border, the other around your property

2) Many governors will impose UK-style lockdowns if the new virus shows up

3) Thus, even a 0.1% chance that a travel ban would stop the virus means the travel ban is an optimal strategy

4) This is true even if the virus is not more damaging than existing COVID

5) This is true even if you think lockdowns are stupid and need to stop

6) This is true even if you think COVID is just the flu - as long as governors don't, it's better to keep the contagious strain in Europe and out of our country