Not at all.
I see the moderator has removed Mr. Vega's post, which is unfortunate. Ironically even though the tone was nasty and yes, offensive to Christians, nothing Vega said was necessarily untrue.
That being said, I do indeed understand that we are in a spiritual battle. That, in fact, is one of the reasons why I think the "Harry Potter is the Devil" hysteria is more damaging to the cause of Christ than the actual book or movie ever will be.
Take a look at the feeding frenzy that any post about Harry Potter starts on FR (do a search, you'll find thousands of posts in the last few days). What is that distracting us from?
For me the biggest problem I have is with Christians who expect spiritual laws and values to always apply to secular situations. In one sense they do, but the use of certain buzz words or phrases just don't play well with those not familiar with spiritual things (the preaching of the cross is to them that perish foolishness).
I just get really cheesed when I see Christians do or say things that damage the cause of Christ. I think in this context, and perhaps in any context, your statement about Mr. Vega being the son of Satan did just that. Instead of softening his heart to the gospel instead it probably made him say "the hell with that, I'm going home to Papa."
I know you didn't mean that and I sense that you are sincere. But we have to think about how our actions and words look to others.