Know ye not that a little leaven leavens the whole lump?
There is also much evidence to support the validity of John 8:3-11. "History Channel Doctrine" has spoiled the Church Body today ... Just because you hear it doesn't mean it's Truth.
I had heard this same thing several years ago. Yes, this does little to alter the fundamental foundation of the New Testament, but it does tend to break down the reliability of the Bible. I think that might be the only reason it was brought to light.
But, what if it is really an addition? How can I be so sure?
My roommate today is a pastor and a Bible and prophecy scholar of over twenty years. He acquainted me with many writings from early Christian authors, many of whom support the existence of this text before others claim it was written. Two of these that I can attest to personally are Papias and Didymus, who both wrote not long after John was exiled.
But in the end, what you believe is up to you.
Love in Jesus,