> The idea that webservers are "all about side effects" gives me a chill. The whole architecture concept of HTTP is no side effects, so to claim that it's all about side effects seems odd. It should only be the case for POST PUT or DELETE methods, and only in very specific ways.

There's nothing incongruous about that. It is the case that side effects should only happen on POST, PUT, and DELETE methods (and the like), but almost all webservers are written because of a need to use these.

If your webserver is all GETs and HEADs, then it is either trivial and you would have used someone else's instead of writing your own, or its sole purpose is to repackage and serve existing data from other sources - a rare use case among all webservers.

If you were to take an inventory of all the webservers out there, you would doubtless find that almost all of them exist in large part in order to create side effects.