People used magic for the wrong ends at that time. It threw the natural order into chaos. Uther made it his mission to destroy everything from back then, even the dragons.
Let this serve as a lesson to all. This man, Thomas James Collins, is adjudged guilty of conspiring to use enchantments and magic and- pursuant to the laws of Camelot- I, Uther Pendragon, have decreed that such practices are banned on penalty of death. I pride myself as a fair and just king, but for the crime of sorcery there is but one sentence I can pass.
When I came to this land, this kingdom was mired in chaos but, with the people's help, magic was driven from the realm. So I declare a festival to celebrate twenty years since the Great Dragon was captured and Camelot freed from the evil of sorcery. Let the celebrations begin!
(There is a loud scream from the crowd)
MCMary Collins
There is only one evil in this land but it is not magic. It is you! With your hatred and your ignorance! You took my son. But I promise you, before these celebrations are over, you will share my tears. An eye for an eye, a tooth for a tooth, and a son for a son!
(voice-over; her letter to Gaius) My dear Gaius, I turn to you for I feel lost and alone and don't know who to trust. It is every mother's fate to think her child is special and yet I would give my life that Merlin were not so. Ours is a small village and he is so clearly at odds with people here that if he were to remain, I fear what would become of him. He needs a hand to hold, a voice to guide, someone that might help him find him a purpose for his gifts. I beg you, if you understand a mother's love for her son, keep him safe, and may God save you both.
(voice-over) No young man, no matter how great, can know his destiny. He cannot glimpse his part in the great story that is about to unfold. Like everyone, he must live and learn. And so it shall be for the young warlock arriving at the gates of Camelot. A boy that will in time father a legend. His name... Merlin.