This isn't necessarily about justice or guilt. They aren't being imprisoned or sentenced. An organization is choosing not to permit them where their members & the public gather, for "protection".

If these individuals were suspected of being in contact with a dangerous contagious disease, you'd hopefully not find it unscientific to minimize risk by telling them not to come to a convention.

But being a child rapist, or ASSOCIATING with child rapists isn't a contagious disease. No, but due to their association to members of a prolific child trafficing ring, they may be considered a higher risk for a certain subset of convention-goers (which claims to offer fun for people of all ages)