Is there a particular meaning to 'active/inactive' that I don't know that justifies your out-of-proportion outrage? What is the problem with observing that 35% of Americans just don't care enough about this subject to go vote ?

Math.

“Half the country voted for X” isn’t accurate math. People just excuse away hard, hard logical facts and it makes me pretty fucking mad.

What a stupid fucking strawman. Was ~35% of the US population in a coma when the elections happened?

We are talking here about people who chose not to vote.

Strictly, yes your cousin is a passive citizen. But no sane human will call them out on that because obviously they had bo other choice.