Night of the Demon - 1957 B&W Horror
As a youngster I remember watching a British movie classic called the Night of the Demon! This was a horror picture based on a story by that master of understated horror, M.R. James. James' story Casting The Runes concerns a mild-mannered man who incurs the wrath of a magician and is passed a slip of paper with runic symbols. If these are destroyed, or are still on his person seven days later, he will die. The crux of the story is the man's gradual realisation that these things are true, and that he must return the runes to the magician to prevent his own death. This particular brand of modern esoteric rune magic has the idea of the yfelrun: this is a usually a letter which when opened is revealed to be a runic talisman devoted to cursing the victim.
Ref: The Grimoire of We-Aze
As I see it there are about three main reasons why runes were considered to be evil. Unable to read or understand the Runes, Christian Clergymen believed them to be magic spells capable of unlocking the powers of evil. Since this time Runes have developed a bad reputation, and are often linked to the Occult and including Satanism. German 19th century Nationalism and anti Semitism paved the way for the Nazis in 1930, who employed the Runes amongst other heathen sigils within their military insignia and propaganda, furthering to promote the sinister reputation of the runes. So runes became associated Nazism. Lastly the New Age renaissance added a whole load of misinformation based loosely on whatever the authors point of view or personal gnosis was at the time to create a whole new tradition, based on in many cases the believed instant acquisition of magical power, hexes and re-invented lore far removed from the actual usage and purpose of these holy symbols.