Cause drones can be jammed/blinded up close. It's much harder to defend from a bullet fired from a kilometer away.

Jamming is easy enough if the drone requires realtime active control, especially if it's on well known frequencies and modulations - but autonomous flight using GPS, 9DOF accelerometers/gyros/magnetometers, and computer vision - is all current hobby-grade reality.

The main reason those are not (yet?) being used for terror attacks is that the skill level required to pull that off is quite high, and the people planning terror attacks seem to find it easier to recruit suicide bombers than geeks.

If any of _these_ guys: http://ardupilot.org/about/team - got "radicalized", I suspect they'd be very difficult to defend against...

Is it possible to jam the drones and not also end up jamming your own communications?

Yes. In its simplest form, radio jamming is just tramsmitting junk on the same frequency as the target. If you want to jam a couple kids using channel 10 on their FRS radios, all you need to do is put your own radio on that channel, ducttape down the push to talk button, and stick it in front of a laptop playing a 10 hour rick-roll video. Jamming RC aircraft, or GPS, or any other radio service is more or less the same in practice. The only difference is the type of transmitter you need to emit the jamming signal.

Radio jamming can be as broadband or narrow band as you desire. The narrower the band you target, the less power you need. The catch is, 1) you need to know what frequency you are trying to jam, and 2) this is not at all legal, so it would probably only fly in the middle of a warzone.

Realistically, a home built drone could be using anything for comms, including the civilian mobile networks or wifi band. Coupled with a tracking directional antenna, such a setup would be very difficult to detect or jam.

Action from distance could allow several drones set to fire on a target from different locations and calculate the projectiles to arrive at the same time.

Yes, and as I noted above, such systems are far less capable than something like a Hellfire missile fired from a Predator drone, so might be preferred to avoid escalation.

This is actually one of the more terrifying videos out there on this subject.