As I said on the other thread, democracies that have "compulsory voting" in secret ballots really have no such thing. You can take the horse to water but you can't make it drink. In the case of voting, you won't know whether the horse has drunk the water or not. Obliging everyone to turn out to the polling station is not the same as making people vote.

There are lots of facets to this. A big worry in some countries (the US and UK are good examples) is low voter turnout. The 2016 US election saw a turnout of about 60%, which was high for America. But it still meant that way below 40% of the electorate voted for Trump. Mandatory voting would be transformative in terms of turnout. The Aussies crow about their 90%+ turnouts. I'd like to suggest that corralling reluctant or uninterested voters to the polling booths, whilst it makes the turnout numbers look impressive, it doesn't necessarily improve democracy (I'm still waiting to hear whether the Aussies crow about excellent governance as much as they do about their turnout).

There's an argument that compulsory turnout would encourage many erstwhile refuseniks to study politics at least a little bit before they go to vote. If that were provable, you couldn't argue that it was a bad thing. Another argument is that, on the whole, wealthier people and older people are more inclined to vote, and vote right wing. More deprived and/or younger people are less inclined to vote but, if they did vote, they would increase the left wing vote. Well that's a deliciously enticing argument for a leftie like me, but there are two issues there: first, it's hardly an argument predicated on principle, and second, it hasn't actually been demonstrated to work that way.

Finally, food for thought: there is no compulsory voting in Sweden (typical turnout in the high 80s), Norway (high 70s) or Denmark (81.4% last time out, and they're worried because that was low!)