I just made the assumption because he's a human.
Per the book that he believes in, there is only one man that was perfect. His name is Jesus and you don't have to be Roman Catholic to accept his gift of Eternal life.
There have been countless examples that show that the RC church (as well as the universal church) is fallible and very easily corruptible. I mentioned the Crusades as one HUGE one. I would say that on the protestant side you have the Westboro Baptists.
In Matthew, Jesus talks about being the only way into heaven. Nothing about conscience. There are plentiful examples in the bible where this idea is confirmed and repeated.
The pope mentions the mercy of God as if it will protect everybody. There are very view, if any, verses to back that up in Scripture. There are plenty of examples of where that mercy is shown through Jesus Christ.
Ultimately, I couldn't tell you if he's right or not. Our culture, and apparently a majority of the planet's, would love to think that God is just going to let everybody in. Which brings up another question "does that mean EVERYBODY or just the 'good' people?" How do we define who is 'good'?
Does anybody see a problem with this? Either murders, child molesters, cerel killers, rapists etc; will also enter or we'll have this gray line of 'a good person'.
God already set that line. It's perfection. And that's where the mercy and Grace steps in. God sent his son, the only man to obtain perfection, to sacrifice himself so that our imperfection would be permanently atoned (paid) for and we would be made perfect through Christ's blood.