I don’t see this as anywhere near the same thing though. These so called ‘donkey votes’ are derided, and categorised as together with voting errors and other invalid voting forms. The right to withhold your vote is as fundamental as the right to withold your labour. Voter turnout is an important metric in its own right, and is observed tactically in, say, the UK.
Compulsory voting simplifies competition, and destroys some forms of it. In particular, the ‘mandate’