Yeah, I'm sure flattening the place and killing hundreds of innocent people is exactly what's needed! Just cut out the middle man and open up an IS recruitment office.
How many innocent people still live in places like Raqqa?
I am sure that as quick as people volunteer, if you strike them down, eventually the remaining people will get the message, but that is only a short term fix, you need to find out who is funding and supporting these "terror" groups and fix that politically.
Personally I feel we brought a lot of this upon ourselves by interfering and launching wars. That was done by certain politicians and they seem to be coated in teflon and can do no wrong. So if our politicians are corrupt how can we ask them to deal with the root causes when it suits their ambitions and aims to take us into conflict after conflict.
In the mean time we need to protect ourselves and if the best way to do that today is using force then apply it and plenty of it, make sure people get the message.