That goes against democracy along with not allowing old people or people in prisons. It is opens the pandora's box to now allowing LGBT or people of color to vote by locking them in prison or fixing IQ tests to yield low scores.
Trump goes against democracy, yet here we are. If we stopped letting the low IQ from voting we wouldn't be in the current situation. Those slippery slopes are all nice in theory, but we are in situation where Trump is president. Sometimes it requires doing things that are in the grey area.
There were about 258mil adult citizens in the USA in 2021( the last year I easily found statistics for), about 248mil of them are 'eligible' to vote. In the 2024 election, about 155mil ballots were cast.
Sure sure... 155mil isn't a small number, but it's nowhere near everyone. 60% of the adult population is a far far cry from universal participation.