The problem I have with mandatory voting is, besides the fact that it would require a national holiday and changes to timing that would already drive up voter participation... given current political behavior in the US it's going to drive a lot of apathy voting to just avoid the consequences that could be more harmful than not.

I absolutely think every citizen should be voting, but it's also not really right to just force them to do it- Give them the resources (time off) and the reason to actually do it, and we'll have turnout of 70%+.