The argument "it's too slow to be a spaceship" makes a lot of unstated economic assumptions. Yes, a bigger sail would be faster. But if you wanted to send a lot

The argument "it's too slow to be a spaceship" makes a lot of unstated economic assumptions. Yes, a bigger sail would be faster. But if you wanted to send a lot of ships to various places, and you were the kind of civilization that makes very long-term investments, smaller probes could be optimal.