Ask an Atheist

Why are Athiests the most vocal in declaring their beliefs?

I don't think atheists are the most vocal. That's a whole separate argument.

Answering from your forced perspective:
Atheists aren't wearing rosaries or crosses, Stars of David, Burqas, or Dastars. You can't just look at us for some physical symbol and know where we stand. Speaking is really the only option we have for making our mindset known. No one really likes listening to someone else explain themselves, but I feel the same way to a small extent when I drive by a billboard with Scripture on it. I guess we have silly symbols like the Darwin fish or the Flying Spaghetti Monster, but eh.

We're just like anyone else, we (wrongfully) think that others operate similarly. If I'm a person who likes a logical argument and can be persuaded by well-reasoned points and sound evidence, I assume the people I talk to are probably like that. But they aren't. Not often.