Harry Potter and the Plot Holes

HT to the Spew Kid for this one.

Harry raises a good question--why let Slytherin recruit more baddies?  I have a similar question: how does Peter Pettigrew make it into Gryffindor? It is pretty clear from the Snape memories that James and Sirius were on their own as they arrived at Hogwarts the first time, so it could not simply be a matter of Peter wanting to be with them--their friendship almost certainly was a result of being in the same house.  Given Pettigrew's cowardice, it is hard to see why the hat would sort him into Gryffindor.

Of course, as Dumbledore put it so well, perhaps we sort too soon.