I've always been a fan of compulsory voting, but you bring up some good points.
(Note that you get around the "sick or on holiday" thing with expanded early voting, which is a major way to expand the number of people who vote).
As for the belief that expanding voting will skew things to the left...in the U.S. I believe that is likely true because of the kind of people the right wing here *try* to exclude from voting. Their goal is to shore up their own power. And somebody like Trump is better at firing up the base than somebody like Biden. (This is not to say we should pick Marianne Williamson *shudder*).
Expanding early and postal voting, bringing ballot boxes TO people who can't go to them, such as people in rehab centers, making voting day a national holiday (and making it illegal to ask somebody to work more than a half shift that day)...and perhaps giving a reward for voting.
I was raised to believe that I had to vote. It was unthinkable not to vote in our household. I also had to deal with a royalist Tory at the same table as a card carrying Marxist, which led to a very early political awakening!
I'm not saying do *that* to your children, but raising them to vote can be done.
Oh, and people?
Vote all the way down the ballot. Please.