I agree that hitting a like button takes no 'work', but I think that's not the point.

The point is to endorse something. It's a social gesture, like typing out the words "I like it".

Zapping is ok, but to a random man on the street, see which of these they would prefer, when you respond to them on something they said:

1. Telling them "Good point, I like it", or:

2. Giving them a fraction of a cent/penny