FatterDumber& Happier Moe wrote:

Wouldn't my vent stack provide a lower-resistance path for sewer
gas vs trying to go through the dishwasher's drain pump?

Ok, so I guess nobody's gonna answer that.

It is possible that an incorrectly installed dishwasher (or
anything) could be contaminated with sewage or chemicals,
then an improperly connected water supply via the plumbing
can back feed to the public water system causing contamination
of the public water supply system.

So how exactly can contaminated water overcome the somewhat high water
pressure of the municipal water system and backfeed into my water pipes
and spread to adjacent houses?

Wouldn't I need

a) a tank of at least 5-10 gallon capacity, filled with dirty water
b) a compressor or pump to take that water and inject it
at high pressure back into my main water supply line
c) the intent to put those items together and make it happen

How else could contaminated water flow back into the water supply
system?

There are lots of examples of this happening. You just might be
drinking your neighbor's sewage or the chemicals he sprayed on
his lawn.

Where did I say that I was on well water? I'm not.