I'm also in favor of joyful practice. Laughter that's appropriate is always appropriate.
Rob, "it's a shame" that you seem to have experienced too many of the "tight shouldered" "emotionally constipated" people that you consider to be "serious" students that shame others. I think it should be really difficult for others to push our buttons. The shame that I have spoken of comes from within. Just like giri comes from within. It's not something that others can require of you. If they do, that's their problem.
I know lots and lots of really serious students of budo that don't fit that picture. We just add a bit of humerous "laxitive" in with their popsicle after practice and they're fine by next practice.
I have heard the types you wrote about described in Japan as being "full of tea" or in the Zen crowd as "bullet heads". Joyful, serious people spot them where ever they're at. It's their way, but not mine.