"I hear the excuse, "it uses too much CPU time", but this is often from people who have written their web applications in Ruby"

I'm curious about this, are these excuses you've heard based on configurations where a proxy server processes the initial https req and then sends the backend request encrypted, too? This is where Ruby is handling an encrypted request?

Or are you saying there are people who have excused https from their setup because their frontend web server is written in Ruby?