Yes, terrible stuff happens, but they are extreme outliers. Not sure how this works, but we can trust strangers to quite a high degree.
I have no experience in the matter, but surely designing viruses is not a simple affair. (In any profession, having a blueprint is not the same as having knowledge, equipment and practical experience; if somebody would try, my bet would be that they would die during early stages of the process, due to inexperience of handling hazardous materials; kind of like Mr Darwin looks after us)