Yes, people that assist terrorists should face as much punishment as the terrorists themselves. They are helping people harm and potentially kill innocent lives. When this happens, the death penalty needs to be enforced. This may not deter all terrorists and their accomplices but if it deters even one, then it is effective.
Treason is the greatest capital crime. Aiding terrorists who kill people, especially Americans, should be punishable by death because it goes against America. It's in the Constitution. Terrorists are the enemies of America, whether they are foreign or domestic. Helping them is just as bad as attacking America in the first place.
I believe that if someone abets terrorists who then commit a violent act that results in death, they should face the death penalty as an accomplice to murder. The United States should make a clear statement that anyone who is caught collaborating with terrorists to harm U.S. citizens and their interests will be dealt with to the full extent of the law.
The punishment should fit the crime, and there is way too much wiggle room on what would be defined as abetting terrorists, to force the death penalty on this. Before going that far, you should clearly define what abetting a terrorist is or isn't. If you can do that and it makes sense, that's one thing, but otherwise I wouldn't be in favor of it at all. There's way too much room for abuse with it.
"Abetting terrorists" sounds like the kind of crime that could mean nearly anything that those in power want it to. The last thing that any supposedly free society needs is some way for the government (that has already become much too powerful) to have yet another way to arbitrarily execute people.