All of Life of Brian aged well. I rewatched the film last year – still thoroughly enjoyable.
What I completely forgot were the scenes with Stan transitioning into Loretta. What seemed like an eccentric joke at the time (more than 40 years ago!) proved fairly prescient. Funny yet handled with kindness.
Well, it does portray a very PC acceptance (fighting for Stan/Loretta's right to have babies even if he/she can't actually have them) even if it is a joke.
So I think it's at least difficult to object to? Yes that behaviour is correct but it's not allowed in a comedy? Stop laughing (so it can still be in the script, it's just not a joke?)?
I think the whole film is far more thoughtful than it is unkind, to any group. The main contemporary objection was from religious groups of course, but just watch https://www.youtube.com/watch?v=CeKWVuye1YE.
It portrays a serious extremist group being derailed by the demands of the furthest, most boundary-obliterating, most ludicrous social extremists imaginable at the time. The fact that that group was later considered centrist doesn't make the joke PC, it just means people don't get the joke anymore.
We can only behave according to what is acceptable in the present moment we happen to exist in, it would be unreasonable to ask people to attempt to predict future morality when making ethical choices. We can try to make a good guess about it and act accordingly but it'll never be perfect, nobody can make a ruler with units that don't exist yet let alone try to measure something with it. I think intent counts in these situations too, like you say Monty Python never set out to be unkind or bigoted to anyone.
Would it be an acceptable sketch today? Probably not, and that's not really a bad thing given that improvements to the rights and recognition of transgender people is one of the more positive things to come out of the last couple of decades in my opinion. Should Monty Python be cancelled over this sketch though? Not in a million years.
"Never Be Rude to an Arab" is Islamaphobic on its face, as well as normalizing other racial slurs.
"I like Chinese" is full of pretty gross stereotypes as well.
The troop claims they harbor no ill intent, and that may be true, but it's easy to say "We're not here to offend" about someone else but not acknowledging the power differences here and why someone might be offended.
What I completely forgot were the scenes with Stan transitioning into Loretta. What seemed like an eccentric joke at the time (more than 40 years ago!) proved fairly prescient. Funny yet handled with kindness.