A couple of days before my presentation I watched this great speech from Jillian York and Jacob Appelbaum (please go and watch this). At some point Jacob mentions that "our security is interdependent".
Few days later Benjamin Mako Hill came to confirm this remark, but with real evidence. He analyzed his emails to find out that despite self-hosting his own mail server, 57% of his emails endup on Google's servers. I ran the code on my emails and I got pretty much the same percentage (and a bit higher if I include all three big providers).
This was how I ended my presentation (not aware of Benjamin's work at the moment):
"I have made a personal choice not to host my email on Google, Microsoft or Yahoo. But if the majority of my contacts use one of these providers then most of my outgoing emails end up to their servers. It's important to understand that our privacy depends on the privacy of our social network."