Well, it was a rather small detail. XD

To be fair, I don't think everything about Voldemort was blamed on Merope. Rowling said he would have turned out differently, but he still was given many chances and opportunities to accept love and help from the people at Hogwarts. Even faced with death, he refused. Still, you're right. Harry feels sorry for her, but Dumbledore might have been a little gentler.

Also a good point on how much she learned.