On occasion the FBI had been known to step on their cranks. Last I checked they are not 100% in court, and have had cases thrown out for defective warrants, improper questioning, etc. They are made up of human beings that are are far from perfect.
And yes, I can picture some junior G-man going out to talk the gentlemen,then things going all pear shaped, suddenly they have 50+ agents crawling all over with all the toys parked and set-up in the driveway and finally the SAC shows up he asks, "So we got a good warrant for all this?" And then a whole bunch of aholes slam shut.
Again, as citizens our job is to insure that those we entrust with enforcing the laws are operating under the constraints we place on them. So asking that question "Did you adhere to the 4th Amendment protections?" is pretty damn important, and not one to be simply assumed.