No, it's not normal to leave so many negs. Some buyers are very trigger happy. Others just seem to have no end of "bad luck" buying on ebay (usually because they keep buying cheap rubbish from Chinese sellers, expecting it to be of the highest quality............because that's what shows in the photos).

One neg isn't going to stop people buying from you. I know it hurts to get one, but it really isn't the end of the world. If ebay refuse to remove it, then leave an honest, professional reply, without emotion, so buyers can see that you are still professional, without getting abusive if there is an issue.