If you think that islamists are united and share a cause you really are ignorant. They spend as much time fighting each other as attacking us.
In any case you are backpedaling furiously now that it is obvious that there have been a whole string of right wing terrorist attacks. By the time McVeigh was spewing his extremist screeds at gun shows moderate people were well aware that extremists in the right could carry out terrorist attacks, it had been well publicized. Nobody was that naive. .
Yet the moderates did not turn him in. Why?
Let's look at the why:
Most likely they were in the exact same relation and situation as moderates at mosques: aware that the guy was extreme and maintaining a distance, not really aware of what he was doing, not really interested to get to know more about it either, just going about their business and limiting contact with the crazies to polite conversations.
That is the reality, its not like the moderates in either case are sitting there listening to details is terror plots, turning a blind eye, they are just going about their daily lives.
We all read canada-man's distasteful, extremist antifeminism but nobody goes running to the police to say he is the next Marc Lepine, but no doubt the next Marc Lepine WILL have spewed similar garbage to moderate people who ignored him: Not everybody with extremist views winds up committing violent acts, most just talk, most people whatever their beliefs just don't turn to violence, either at a mosque, on terb, or at the gun shows McVeigh attended. At the gun show period listened to McVeigh and gave him the benefit of the doubt, just as they have with many other extremists there who didn't go on to blow anybody up.
Saying that moderates at a gun show or a mosque should be blamed for the acts of extremists who pass through their organizations is too much: the moderates likely self limited their interactions with the extremists to pleasantries and didn't have any incriminating evidence, and didn't look for it either.
Were the gun show moderates to be blamed because that didn't dive in to find out how serious McVeigh was? Because instead of sitting down to investigate him, they just smiled, nodded, and moved on to the duck hunting booth? How is it different for a family taking their kids to the mosque who crossed paths with the SB shooters?