I'm not saying I disagree with the idea of mandatory voting, per se. But in the U.S., a fine for not voting would quickly be labeled a "poll tax", which would immediately raise the connotation of being racist in nature. In a day or two, the whole idea would be scrapped on grounds of unfairly targeting minorities and the lawmaker who suggested it would be accused of secretly being affiliated with the KKK.

I'm not saying it's right, but it is what would happen.