It wasn't McQeary's decision to give Sandusky access to the PSU athletic facilities...that was either Paterno's decision or someone else's. In McQeary's case he did what (in the mind of a 28 year old graduate asssistant) was rational...he reported it up the line. The fact that someone at a higher level continued to give Sandusky access to the school isn't McReary's problem.
The fact that McQeary discussed this with his own father and with Paterno is an indication that he was struggling with the issue and trusted that it would be dealt with correctly by those in the administration.
McQueary had the evidence of his eyes that it hadn't been dealt with correcty.
McQueary knew the culture at PSU protected Sandusky. McQueary went along with the cover-up and was rewarded with a coaching job.