What is it still claimed that there is "no cure for the common cold" why is this?

See below. Because colds or viral upper respiratory infections are self limited and resolve on their own, any treatment would have to be extremely safe with no potential serious side effects. Most anti-viral drugs have the risk of serious side effects which prevent them for being used against this annoying but benign infection. Hopefully one day a safe and effective anti-viral treatment will be found.