@BillRM,
Yes, I do think that. Most people are too lazy to follow simple directions, let alone look up those directions. Mentally ill people, unless they are compulsive have no more reason to be competent than the majority of people.
I know someone, now deceased, that used to routinely substitute spices when baking with another spice that was the same color if they didn't have the correct one. Cayenne pepper in place of cinnamon makes for an "interesting" cookie but it isn't following simple directions. These are the kind of substitutions lots of people make when following simple directions. Don't have detonator cord. Heck, just soak some string in gasoline. It's gotta work.
McVeigh experimented with making bombs before he loaded his truck. Andrew Kehoe was referred to as the "dynamite farmer" before he blew up the Bath school because of all the explosions he routinely set off on his farm. Most people don't make a working bomb in their first attempt. We have seen many instances of people going on killing sprees and also having bombs of some type where the bombs never explode. Harris and Klebold originally planned to blow up the school and kill responders with another bomb. Their bombs made following simple instructions didn't explode.
If all these mentally ill people exist in society then why aren't they currently making all the bombs you insist they would? You keep insisting bombs are a more deadly choice and they are easy to make.