Mandatory voting just adds semi-random votes, skewing the proportion of people who are really voting for their own interests, but rather out of vibes due to obligation. Holiday on voting days and repealing of disenfranchisement measures work much better.
One minor twist: the legislation mandates that one reports to the polling center. The uninformed can select "none of the above" if they are not sure what would be best.
I think it would still encourage meme voting in retaliation for having to show up. "You can force me to do this but you can't force me to do this in good faith."
If the worst you can say about this scheme is: "people may vote randomly" I don't feel that bad. I assume the amount of people that spite vote(!) would be greatly outnumbered by people that actually give a shit (but who may not be able to vote today, due to work obligations)
The reason I think mandatory voting in Australia is nice (tiny fine for not doing it, so turn out is like 85-95% every time) is that because everyone obliged, it keeps voter disenfranchisement politically difficult. When you go to vote on election day, you wait 20 mins, tops, usually less, and you can vote ahead of time via mail or in person. It's always Saturday for this reason too.
I'd argue it's this easy partially because everyone HAS to do it, so if politicians start making it hard, people are gonna be pissed very quickly, so no one messes with the well-oiled machine.
And there are no stupid "get out to vote campaigns" wasting valuable headspace where instead we could be talking about actually issues.
Australia's electoral system is far from perfect (single member local electorates which basically guarantees two stronger parties), but mandatory voting is definitely a feature I do not want to be rid of.
it keeps voter disenfranchisement politically difficult
Voter disenfranchisement, and mandatory voting are mutually exclusive concepts. One does not have the right to vote if they are forced to vote. Having a right encompasses the freedom of choice.
It doesn't "just" do that. It totally reverses the ability for governments to block people from voting. If it's an obligation then people must be provided a reasonable chance to vote. It makes more people engaged in politics as well instead of "can't be bothered"