I largely agree with Dave, but it's important to think about what you wish the alternative to be. If you ban laptops from meetings, what do you do when people pull their phones out? Are you going to ban phones from meetings too? What about daydreams, are you going to ban those too?

I remember being in a military course where we were getting very little sleep, and naturally, there were no personal laptops and personal phones were banned. If people started to nod off from the lack of sleep, they were called out and asked to stand up to keep from falling asleep. Does anybody really want to work in that kind of environment where their attention is not invited, but commanded?

Sure, it's important to make sure people are focused in meetings. But the way to do that isn't just by setting a positive example, but by increasing the focus of the meeting: reducing the number of invitees to only those who are really necessary, having a scheduling framework for who is expected to talk about what and for how long, and making sure that everybody in the meeting is focused on producing, together, the documentation (e.g. a record of the decision made) which is the product of that meeting. People are a lot less likely to "slack off" in meetings if they feel like their presence is necessary, appreciated, and productive.