Point taken. Why 30min though ? it's usually said that you'd need 45min to reach the deep fat burning. (from little experience, my body really reacted differently after 40minutes)
At the end of the day, if 7 minutes of cardio is all you can stand to do, you're screwed.
The patronising attitude isn't going to help anyone who has gotten that far out of shape.
Even if someone is sufficiently unfit that they can't do more than 7 minutes of cardio work in a session, they still have to start somewhere and build up. The alternative in most cases will be their fitness decaying even further.
Keep in mind that there are a lot of reasons people might be that unfit. Some will just be lazy. Others might be recovering from a serious injury or illness, and just being able to walk for five minutes to get to the shops unassisted is a big achievement.