There's a dangerous consequence to saying this. Here's how:
1. Voting is easy.
2. Voting is valueable: it literally changes HN for everyone else.
3. Agreement/disagreement is easy: we're taught how to do it as children.
4. Agreement/disagreement is value-less. Saying that you agree with pg on 'Hackers and Painters' is valueless. Saying "prior to reading H&P, I was in mindset A-B-C supported by points of view D-E-F, and here's how they were modified, and here's the new mindset H-I-J" conveys the same agreement, but it provides value.
We shouldn't incite people to use up/down votes to express something value-less. Agreement and lack thereof (alone) is valueless.