When I first moved to Australia I rankled at compulsory voting as I believe that not participating is a valid political act. Countries without compulsory voting talk about the turnout as relative to previous years, and if it falls too far there will be questions about a mandate to govern.
In Australia that can't happen as turnout is always high, this leads to very little opportunity to overhaul the mechanism of elections to make it more applicable to the community, or to overhaul political parties entirely. Red team or Blue team are guaranteed some high proportion of the country voting for them and it gives a false sense of relevance.
However I'm now fully in favour of compulsory voting. Why?
Look at America, what an absolute shambles of a democratic system. One party spending decades attempting to stop black people voting. Voter suppression and gerrymandering (also not possible in Australia) baked into the political system. No thanks.
Australian politicians are no better, they would reach for those tactics in a heartbeat, compulsory voting stops us from heading down that path. There is no utopia, the system has problems, but the trade-off is worth it.