Detect the logical fallacy here

In Hyde Park, England there is an area called Speakers' Corner where open-air public speaking takes place. Sometimes the various debates get really heated but no one is harmed. Recently, however, during a debate, a Christian apologist was stabbed, apparently by a Muslim, but we don't know the identity of the person as of now so we cannot say with certainty the background of the stabber. Footage shared on social media shows someone dressed in black approaching a woman wearing a Charlie Hebdo T-shirt. How many Muslims would wear a Charlie Hebdo T-shirt?

With that background being provided, the following debate has emerged (I won't use names here). 

Christian lady was stabbed in the course of a debate, allegedly by a Muslim.
Muslims cannot enter a debate without committing an act of violence.
Thus Christians are rational and Muslims are irrational.
Therefore, Islam is false and Christianity is true. 

That is the crux of the argument being circulated. What is the logical fallacy here?  

This "argument" is full of non-sequiturs and questionable premises. It's just bad.

Christian lady was stabbed in the course of a debate, allegedly by a Muslim.

Probably the only okay part of this 'argument', although I'd like to know who is doing the 'alleging' to test their reliability.

Muslims cannot enter a debate without committing an act of violence.

Double non sequitur because 1) even if the stabber is Muslim, it does not follow that Muslims in general are stabbers and therefore violent (this is a hasty generalization) and 2) we did not ascertain the religion of the stabber - if they even have one - so this premise has no relation to the previous one.

Thus Christians are rational and Muslims are irrational.

Another non sequitur because we haven't said much about Christians (other than the fact that the stabbing victim is one). Even if we grant the  truth of a very questionable second premise, we can't infer that Christians are rational - in fact, we can't infer anything about them.

Therefore, Islam is false and Christianity is true. 

Glaring non sequitur. That adherents to a belief system are irrational does not imply the belief system itself is irrational, or that its conclusions/predictions are false. This is because belief systems are pure, but the people practicing them are not (instead coming from a host of cultural, economic and geographical backgrounds which all determine behaviour, completely separate from the beliefs themselves).

Who in their right mind would promote such garbage? Lol.

Wow, where do I begin?

I think Rationalissimo covered most of the bases. However, I'd like to point out that there there have been far too many acts of violence conveniently blamed on Muslims. Consider the school girls that were allegedly blown up by the Taliban recently, for example.

The Taliban have long had enormous power in Afghanistan. If they wanted to blow up school girls, they could have done it two decades ago. So why would they blow up little girls at the very time the U.S. is retreating from its latest failed war?

So when you say a Christian was stabbed "allegedly" by a Muslim, I have to question the story's credibility from square one.

Does your second sentence begin with "Therefore"? In other words, are you saying that this lone incident proves that Muslims cannot debate without violence? If if there is no implied "therefore," that would be a ridiculous assumption. Muslims engage in peaceful debates all the time, while Christians can be incredibly violent.

Christians are rational, Muslims irrational? I'm among the many people who avoid religious fanatics in general.

"Therefore, Islam is false and Christianity is true."

What do the words "false" and "true" mean? Scientists have found no evidence to back up the biblical claim that the Jews were held as slaves in Egypt. Nor is it likely that some weirdo who roamed the wilderness talking to burning bushes actually parted the Red Sea. I'm not familiar with the Koran, but I suspect it has some "interesting" stories as well.

In summary, that argument you shared is so unhinged, it doesn't even qualify as an argument.

"Muslims cannot enter a debate without committing an act of violence." Hasty generalization

Lets change some wording to make it more clear:

White lady was stabbed in the course of a debate, allegedly by a Black person

Black people cannot enter a debate without committing an act of violence.

Thus White people are rational and Black people are irrational.

You are basing the whole group on one person.

"Footage shared on social media shows someone dressed in black approaching a woman wearing a Charlie Hebdo T-shirt.

How many Muslims would wear a Charlie Hebdo T-shirt?"

This is a red herring. Asking how many Muslims is totally irrelevant. Plus, It's not unreasonable to consider a would-be Muslim attacker might adopt some sort of disguise -- and what could potentially be more disarming than a vengeful Muslim in a Charlie Hebdo T-shirt?  Or maybe he was commemorating the Charlie Hebdo massacre as a triumph of jihad. Either way, the question leads us nowhere.

As far as the rest of the OP, I see it being more of a Possibiliter ergo probabiliter, or Appeal to Possibility. See Dr. Bo's Appeal to Possibility.

Logical Form:

X is possible.

Therefore, X is true.

X is possible.

Therefore, X is probably true.

The idea that the attacker was Muslim is certainly possible but that in no way makes it probable. 

As for the rational Christianity v irrational Islam argument - that's just a hotchpotch of confirmation bias and maybe a bit of part to whole fallacy.

Christians are less violent and more rational than Muslims ( Are they?)

Therefore, Christianity is a better religion than Islam. ( Now, that's definitely debatable.)