I have a question regarding the disputed texts in the Bible i.e. the Adultery Pericope, the extended ending of Mark 16 and the Comma Johanneum. I've encountered some Muslims who try using these disputed texts in the Bible to prove that the Bible has been corrupted. While I'm aware that there is overwhelming consensus that supports the fact that the Comma Johanneum is probably a later addition to the Bible (and as such many modern Bible versions have removed it), the same can't be said for the Adultery Pericope and Mark 16, where there are still strong arguments both for and against retaining them in the Bible.
Regardless of whether these two parts of the Bible are original or not, what I'd like to know is how should I respond (and how you would) if Bible critics and especially Muslims use the Adultery Pericope and Mark 16 controversies as ammunition to prove that the Bible has been corrupted, unlike the Quran. According to them, since even Christians cannot agree if these two parts of the Bible are original, what is there to say that the Bible, even if just in parts, hasn't undergone corruption that has gone undetected over the centuries? And sometimes they may even cite the Comma Johanneum as evidence that corruption has crept its way into the Bible in the past.
First of all, we need to recognize why it is that it is so deeply essential for Muslims to claim the Bible is corrupt. It is not just that they want to convince people that the Qur’an is better than the Bible. They claim that their scripture is inspired, obviously, but they also believe, because the Qur'an tells them to, that Jesus was an inspired prophet. The problem is that what the New Testament reports Jesus as saying, and, more importantly what it says about what Jesus did is in diametric opposition to the Qur’an. If Mohammed is right, then Jesus did not die on a cross and his claims to be God are unequivocally false. So, Muslims cannot have it both ways. Either the Qur’an is not inspired or the New Testament is corrupt. If the New Testament is not corrupted, then the authority of the Qur’an, logically, collapses. You can see how much is at stake. For this reason, Muslim apologists have no choice but to go after the Bible. The problem is that the evidence does not go where they want it to go. Remember, for them the New Testament has to be REALLY corrupt!!!! The story of Jesus dying on the cross has to be a corruption, as does nearly all of the statements of Jesus about himself in the Book of John. If the Qur'an is inspired, then the entire story of the crucifixion has to be a third or fourth century invention. This would be a lot of corruption! The problem for them is that there is no evidence for such corruption. None at all.
Here is the rub. First of all, 1 John 5:7-8, John 8:1-11 and Mark 16:9-20, as you point out, are quite simply not corruptions. They were not part of the original. It is possible, but not likely that John 8:1-11 was in the original, but whether it was or not, this does nothing to show that the undisputed parts of the New Testament, which makes up more than 99.5% of the text, is certainly not corrupted. We know this because of the overwhelming manuscript evidence and the literally thousands of quotes from the New Testament from Church Father authors in the first through third centuries. Even if John 8:1-11 is a corruption (it is not) how does this mean that Jesus did not claim to be God or that he was not crucified? This is a leap of gargantuan proportion.
The fact is that we have nearly 8,000 ancient Greek manuscripts, as well as well over ten thousand ancient Syriac, Coptic and Latin manuscripts, making our ability to reconstruct a nearly perfect original Greek manuscript extremely strong.
There is a deep irony here. Muslims claim that their scripture is perfect, yet they completely deny any attempts to discuss whether this claim holds up to the evidence. The caliph ‘Uthman created a unified text of the Qur’an in the early eight century and systematically saw to the destruction of all competing versions of the Muslim scripture. We know for a fact that there were competing versions because a very small number of manuscripts of competing texts survived the attempt at covering up the variations. The Sanaa manuscript (discovered in the late 90's) is one of these variations. It contains a slightly different list of suras. The differences with the ‘Uthman text are fairly small. They are on a scale not all that different from the three supposed corruptions you mentioned. The problem is that if you try to bring up these textual issues you literally risk being killed for having the gall to mention the scholarly issues around the Qur’an. I am not exaggerating here. When the Sanaa manuscript was found several years ago, not a single Muslim scholar had the courage to even study the manuscript. It had to be studied by British scholars!!! This is an absolute embarrassment and proves the utter hypocrisy of Muslim apologists who claim the Bible is corrupt.
Here is the bottom line, the evidence for the reliability of the New Testament is vastly stronger than the evidence for the reliability of the Muslim scripture, yet these apologists, in a desperate attempt to prove a lie, ignore the problems with their own scripture and trump up the weak arguments of atheists and other anti-God critics in order to hypocritically attempt to destroy the faith of Christians who certainly are not going to accept the weaker claims of Islam.
Muslims live in an evidence-free zone. This is what you should share with your Muslim friends.