I just want to remind people that espionage happens both with immigrants and with natural born citizens. Same thing with terrorism. Lest not forget Robert Hanssen or Timothy McVeigh as examples of real homegrown spy and terrorist. We of all should not fall in the trap that because a few immigrants do bad things, all immigrants should be scrutinized much more than the common population.
For the other questions I am sure that intelligence agencies are experts on bringing people aboard with a mix of patriotism, grievance, money, threats, whatever it works. If you have access to valuable information chances are somebody is going to get it from you, with or without your collaboration.
Furthermore, the media helps on keeping the spotlight more focused and brighter on immigrant cases than in American cases. The guy (white American for all I know) who almost died of ricin he was making and keeping in his motel. The media bent backwards to try to say that wasn't terrorism related. If it had been a muslim with the same ricin it would probably be reported very differently. Please allow me to quote something from the media about this case:
"Officials have said they've found no contamination anywhere, and no link to terrorism in the discovery of the exotic toxin, which can be lethal in amounts the size of the head of a pin. Ricin has no antidote and is legal only for cancer research."
I think there is strong bias against immigrants in media and in society and we should do all in our power to show that immigrants as a whole are very law abiding people who contribute very positively to society. There are bad apples, but their amount compared with the larger population is probably of a lower percentage.