The Logical Fallacy of "What if Everyone Said That?"

I am really bothered by this argument, and I hear it a lot. The argument goes something like this:

A: "I don't want to vote because I don't feel as if my vote will count."
B: "Well, what if everyone said that? Then no one would vote! Therefore, you should vote."

In case you can't tell, this argument is rather flawed. It's structure is as follows:

A: I want to do X.
B: If everyone did X, the result would be bad. Therefore, you shouldn't do X.

This argument makes no sense. Your actions are clearly not going to change everyone else's actions.

Example: replace "do X" with "eat a tunafish sandwich":

A: "I want to eat a tunafish sandwich."
B: "If all 6.7 billion people on this planet ate tunafish sandwiches, then there would be no more tunafish! Therefore, you shouldn't eat tunafish sandwiches."

See what I mean? It's ridiculous because whether or not you do some action, others will do otherwise.