Stallman's argument assumes there is an equivalent non-SaaS version of every service or that you should live without it if you can't get it as open source. I am giving up absolute control to use Google's search engine but it is not practical to build my own system to index the entire web with sub-second response times. If there was a distributed open source search engine project where a large number of people could pool resources to recreate something similar to Google that would be a different story.