I don't care how secure these mainland prisons are. That is not the point.
Once the terrorists are on U.S. soil they will be eligible for our civilian court system and will use it as a platform for spouting their ideology. I don't want to give them that publicity.
Most important, the rules of evidence in a civilian trial., which can't ever be met, will favor their release into U.S. communities when the cases fall apart in civilian court. GW Bush had many faults but the one thing he got right was not bringing these terrorists onto U.S. soil.