I don't use the term whataboutism in my post anywhere. So I don't know who you are quoting.
The not serious person here is you, saying we are all going to die anyway instead of encouraging people to do anything. I had to look this up as I don't know anything about Carter, but it turns out the panels he was installing are for hot water. They don't generate electricity. This makes perfect sense as it took much longer than that to develop photovoltaics and get them ready for mass production. Even now modern photovoltaic panels are fairly inefficient devices.
We already have walk-able cities in much of Europe. It's not a compete solution by itself, we still have cars. You are weirdly fixated on USA history when this is a global problem. It's not all about the USA. Stop pretending it's the only country that exists. India and China are the biggest polluters these days if I remember correctly, you should be focusing on them.
Edit: Carter was also aiming for 20% of energy in the US to be made renewably by 2020. That wouldn't have been anywhere near enough to stop climate change.