Swap "costly" for "mildly inconvenient" and then I could almost see where they're coming from but I think they're missing the forest for the trees here. Let the "like button" die, rulings like this take the wind out from beneath it and eventually it's a metric you'll never be burdened with.
Either they take a stand against holding all businesses liable for transfer of data, or those who pay them a membership fee will see an increase in liability or a decrease in the perceived precision of advertising data.
They're not missing the forest for the trees. They're busy logging the forest for the trees, and would very much like everyone to hear their call to action and join their side.
One solution would be to have a "turn on like" button, but the image solution that some comments point out seems like a good option as well
(Or fb could have data sent only when the person clicked the button, but that's unlikely to happen)