With the players who were named in the Mitchell Report, one of the common refrains is: "They had an opportunity to defend themselves to Mitchell himself, and they didn't take it. Therefore, they are more likely to be guilty."
Allow me to try and apply the same scenario elsewhere to demonstrate why this reasoning is fallacious.
Let's say that you work in a company of 3,000 employees. Management has been concerned for a while that there has been a large amount of theft from the company occurring by employees. To counter this, they hire a well respected investigator, Marge Gitchell, to try and uncover the culprits. Marge immediately sends a company wide email urging employees to talk to her about the large amount of thievery going on in their ranks.
You glance at the email briefly, and then move it to the trash in your email client. It's not really your concern because you don't steal from the company and you don't pay enough attention to your officemates to know if they are stealing either. You feel that you have nothing to add by talking to Marge.
A few months later, you are shocked to find that Marge has listed you on her report as a likely thief. Fellow employees and management are outraged. Heck, it's even on the local news, and everyone wants to know why you didn't defend yourself to Marge while the investigation was ongoing.
What are you going to say?