In my experience, strident assertion happens with all beliefs, not just atheism and faith. I associate it with insecure belief, someone who is still trying to convince themself, who can’t defend their position, so they go on the offensive instead. Puppyish enthusiasm is something quite different.
Speaking as an atheist, I do have fun when happy clappies (apologies if anyone finds that term insulting) or god botherers (similarly; it’s not an atheist term, but a british one) try to convert me. I tell them I’m beyond hope, I don’t believe in pixies, but then I wish them immense luck and tell them what they’re doing is essential. It seriously confuses them, and they usually then leave me alone. My point is genuine, too: there are some people who can’t live with doubt, whom religion can help by giving them an anchor & a guide in their life. If the prothlesizers can find such people, they can do them a power of good.