User blog comment:Ḡwẵine Ḹٍٍkƨ Ĺiĸe Ͼềлȑềd/WORST plot hole in the HISTORY of 'Merlin'/@comment-5102537-20121015094558

If you take a look at the transcript of The Beginning of the End, it is obvious that Arthur knew very well about Mordred either having or practicing magic:

ARTHUR The Druid was only in Camelot to collect supplies. He meant no harm. Is it necessary to execute him?

UTHER Absolutely necessary. Those who use magic cannot be tolerated.

ARTHUR The Druids are a peaceful people.

UTHER '''Given the chance, they would return magic to the kingdom. '''They preach peace, but conspire against me. We cannot appear weak.

ARTHUR Showing mercy can be a sign of strength.

UTHER Our enemies will not see it that way. We have a responsibility to protect this kingdom. Executing the Druid will send out a clear message. Find the boy. Search every inch of the city.

Then later:

ARTHUR He's just a boy. What harm can he do?

UTHER He is a Druid, and that makes him dangerous.

MORGANA The Druids would see your father's kingdom destroyed.

ARTHUR I had no idea you were such an authority on Druids.

UTHER Morgana is right. Double your efforts.

And:

ARTHUR Perhaps imprisonment is a more suitable punishment for the boy. I mean, he's so young.

UTHER It would allow him to grow more powerful, more dangerous, until he strikes against us.

ARTHUR We don't know he's gonna strike against us. He's yet to do anything.

UTHER It is enough that his people conspire to overthrow me. This is harsh, but necessary. I take no pleasure in killing the boy.

ARTHUR Well, then spare him for Morgana's sake. She's clearly grown attached to the boy, and if you execute him I fear she will never forgive you.

_________________________

By now Arthur should know even more about the druids. As for Arthur probably had forgotten about Mordred, it's very unlikely because it was not only a memorable event when he saved Mordred and handed him over to the druids but he also would have asked Merlin in the latest epsiode who Mordred was since Merlin remembered him very well. Making Arthur forgetting about saving a druid boy and hence going against his father would only make him the most ignorant and stupid person ever. It's really quite unlikely.

Let alone that before making Mordred a knight, even if Arthur is unsure wether Mordred has or uses magic or not, he would test him first, wouldn't he?

It's all such a great big huge plothole, I actually can't believe they did it that way.