[whoopdedo]

Mandatory voting would give a lot of power to the gerrymanderers. As we know, modeling the behavior of large groups of people is easy. When you can predict who will vote and you have access to drawing voter district boundaries, you have the ability to preselect who will be elected.

Not voting is a choice and allows voter apathy to play a role in deciding elections. If an area is a majority Democrat but most of the voters don't care enough to vote then a motivated minority party can put boots on the ground and get their candidate into office. With mandatory voting that would never happen as the majority incumbent would always win thanks to receiving all those votes cast out of obligation rather than intent. That aggravates the most difficult part of democracy which is giving people with unpopular yet valid opinions a voice in the conversation.

Now, if we had proportional representation...