The 'no true scotsman' fallacy is a favourite. "These aren't true muslims/christians/whatever' when one of them commits a scripture-justified atrocity. Well, I've understood the fallacy to be if you go from a general set to a specific case/token, and then ad-hoc that the specific case/token is not a member of the general set, so as to cover the specific when it mismatches the generalised claims. So Chrisitans usually say theirs is a religion of love, but I say, Matt 10:34 contradicts that claim.
Let me see.
If Matt 10:34 says 'I bring the sword', then this is a specific case that violates the 'general' case of putative NT benevolence. So I'd have done the TS fallacy in this case if I'd said something like: "All verses in the NT are loving, Matt 10:34 is not loving, therefore Matt 10:34 wasn't authored by Jesus or is not a true Christian verse." This of course assumes that 'christian' necessarily means accepting every verse in the NT. I believe I've done the reverse; I've said: Here's a specifc case of a non-loving verse, which means that the general case/claim "NT doctrine is loving" is not completely true. The 'scotsman fallacy' would be to try explain 10:34 away or redefine christianity so as to preclude 10:34 from being 'true'. So, symbolically...
For all Scottish S, it is true that they don't take sugar in their porridge (~P)
Alasdair, born in Glasgow, (A) does take sugar in his porridge, (P), therefore A isn't Scottish (~S)
Interlocutor's claim: for all S, S: ~P (a possibly false generalised premise)
My objection: A, A: P
Interlocutor's false conclusion: therefore A: ~S
This might even generalise as [S -> ~P, P, therefore ~S] or [ S v P ]. (Am I right? - I'm not sure. If it's Sunny, then it's not Precipitating. It's precipitating, therefore it's not sunny. That seems generally true.)
But since A was born in Glasgow (presumably necessary and sufficient for being Scottish), S, which contradicts S, S: ~P, it seems to follow that
A necessarily: S
so all that we've established is that there's a contradiction between
A necessarily: S and
A, A: P -> A: ~S
The fallacy is when you reply "well in this case, sugarless porridge overrules Glasgow", no?
So if no true Christian would say/do something vicious (C, C: ~V)
I ask for an explanation of Matt 10:34, call it M, M: V (vicious Matthew).
Interlocutor: for all C, C: ~V (a possibly false generalised premise)
to which I reply: M, M: V,
To which my interlocutor has to reply: therefore M: ~C
Which suggests that arguing that M is not christian is a scotsman fallacy. A, A: P, therefore A: ~S
where I have
M, M: V, therefore M: ~C
Which is analogous.
So to reply that Matthew 10:34 doesn't represent christian values is a scotsman fallacy. One has to abandon the first premise that (P, P: ~S) or (C, C: ~V) - ie accept that to be christian is to be sometimes vicious, and to be scottish is to sometimes put sugar in your porridge.
Incidentally, the context of the verse is about giving up your family to follow Jesus, it’s not specifically about violence.