Many sources site GRE as supporting broadcast/multicast and IPsec does not. Both GRE and IPsec are merely tunneling protocols. Therefore there is nothing inherent about tunneling protocols which prevents Multicast/Broadcast.
What is it specifically about IPsec that does not allow for Multicast/Broadcast traffic to flow through the tunnel?
By comparison, it might be also helpful to also answer: What is it specifically about GRE that does allow for Multicast/Broadcast?
Best Answer
GRE and IPsec aren't one-to-many technologies. Thus multicast/broadcast doesn't have much meaning. That said, there are ways to push multicast across either system -- both sender and receiver -- but few systems actually support it. It's far easier, and less headache, to setup multicast routing.
(This is even more true when tunnel interfaces are being used, i.e. routed interfaces.)