Therein lies the flaw with value for value. What you may find great value in and zap accordingly, someone else may find less value so they zap less. That isn’t the issue, it’s how people judge others who zap less, that creates a whole other dynamic that people don’t need to be dragged into.
A real world example would be if you’re walking down the street and there is someone on the corner playing guitar and their case is open to accept tips. Now, the five people in front of you just tipped him $5 each. There are many reasons why they may have given that much, maybe they are just generous or they truly found value in the music. Now, here you come and you drop 50 cents in there. Does that mean you didn’t find value in the music or that you just didn’t have the 5 bucks to give or both? The problem is, from the outside looking in, you could be perceived as cheap because you didn’t match what others gave when the reality is one of those other two options I just mentioned. And from the musician’s POV, he is probably wondering the same thing.
For this reason, zaps should only be made on your profile page, with the sender remaining anonymous. Same real world example, imagine if that same guitarist had a box with a slit at the top, then nobody knows what anybody else gave so there is no pressure to feel obligated to match it and the receiver doesn’t know either, so there is no judgement from him/her.