What if I was receiving data to the Arduino and I had RX pulled low at that time by a switch. It would present a short to the output of the programmer. Not good.
I think that maybe to use RX as an input, I should use a 1k res->switch-GND from RX pin. Set the chip to pull up pin 0.
To use TX as an input, same thing, in case TX was enabled accidentally and my switch was pulling TX low. Set the chip to pull up pin 1.