Here's what I found: so many terrible videos such as this one and various websites which make the same fatal error (thankfully a site like this one does slightly better: BBC World Service Learning English).
It is totally, totally useless to teach forms to students without a context for how they can actually use it, in real-life. Thankfully, Touchstone does quite a decent job of it and for the chapter on passive modal verbs, they have chosen rules and regulations as the topic, which fits nicely together. The students can talk about things such as legal drinking ages and at what age people should get married. It's not often that I have occasion to rant about how English grammar is taught to students who are learning English, but this one makes me feel so distressed. SO distressed. Am I the only one who feels that many teachers are doing a huge disservice to their students?