Sometimes, you want to forget that people had an opinion. Or just posted a lot of spam. Either way, you're reading this because you want to get rid of comments in a WordPress WXR export.
sed -i '/<wp:comment>/,/<\/wp:comment>/d' *.xml
On OSX? The installed version of sed doesn't support -i, so you'll need an alternate version. Here's how to install it with Homebrew - http://brew.sh/ -
brew install gnu-sed --default-names
Update your .bash_profile to include gnubin in your PATH: