If he hadn't come to Camelot, everyone would still be alive.

Hm. Now that you mention it, this entire series if basically Merlin trying to fix his first mistake of coming to Camelot at the start of the series. So even when he saves lives, it's mainly because he put them in danger in the first place as it's just one long chain reaction from Merlin stepping foot onto Camelot. Huh.