At an individual, probably nothing. But at a macro level, apathy is equivalent to a lack of legitimacy, which is a big problem. If the cancer of apathy spreads too far, the entire system comes crashing down.
It’s like a party where your job is to bring one of the mixers. You don’t bring yours, nothing that terrible happens. No one brings any, and the party becomes a disaster.
Well... yes. And I view this as a good thing. The current US voting system is broken and I am not sure it is fixable simply by voting more - that simply entrenches the current system.
I prefer to use illegitimacy and disenfranchisement to spur useful change to the systems themselves. I want to see somethink like ranked choice with an instant runoff, the abolition of the electoral college and a simple one person, one vote choice for president, without dividing people into small groups first.
Reforming the senate is likely also a good idea.
Apathy and illegitimacy are the kindling needed to foster real change.