Networking among Internet professionals is alive and thriving. Competitors A savvy business person promotes their service and products without blatant, in your face, billboard style messages. If you have recently shared information about your services, on the open group, respond to following leads for your services. Mass mailed messages to private e-mail, Usenet or Mail Discussion lists is considered Spam. If you are Spam you will be permanently filtered out of many in-boxes and your professional reputation on the Internet will be darkened in the most profound of ways.
Flames are a public confrontation.
There are people out there seething with anger and frustration. They apparently have plenty of time on their hands and not much to lose. You do have much to lose by responding. So just don't. Not even to defend assaults or accusations.