Of course it is slander to say that somebody's reputation is damaged. Especially when it's not a public figure. Just that somebody's name is public, doesn't make them a public figure. And you even continue. Step out of the mob frenzy for a while and try to look at how you are behaving from a higher perspective. Is it right of you to treat a person like that, because he sold his own business? It matters little you once purchased a product from him. Software change owners all the time.
Until there is definite proof of malevolence you should calm down, as should the other hackers. This business has the possibility of becoming a great embarrassment for Hacker News in the future.