I wouldn’t say that compulsory voting is “stupid”. There are some very good arguments for it.

Firstly, it addresses the imbalance of cost of voting (the time and effort you need to spend to cast your vote) with its effect (the tiny fraction of impact your vote has on the outcome). This disproportionately affects lower income voters, especially in some countries like the US, where voting usually happens on a weekday.

Secondly, the outcomes are no longer won “by turnout”. In other words, to win the election you can no longer merely convince your supporters to vote for you, you need to actually convince people who don’t support you to vote for you.

Thirdly, and perhaps less convincingly, this stimulates the interest in the decision and the outcome. Since you have to vote, you may be inclined to actually form your opinion about the elections, and follow up on its outcomes.