After my first book was published, I was getting some vicious and irrational criticism from a speaker. I asked Walter Martin for his advise. (He had endorsed the book.) He said that given that this person was somewhat influential, I should send him or her a registered letter in which I rebutted all the charges, and then drop it. Then he said, "You can fight a skunk and win--but who wants to?"
I have not aways lived up to that sage advice, but I am trying. On the Internet, there are hordes of skunks--those who take cheap shots, don't use their real names, insult without arguments, and so on. So this should be kept in mind.