No don't be ridiculous, only most of them.
Especially the ones attended by middle-class, well-off, arseholes and entitled pricks, with more money than sense who can't be arsed to take their shit home with them.
And...
a; No they don't claim to be carbon neutral but they do make a whole load of other claims about their 'green' policies, and requests about attending the festival - requests that are clearly ignored such as not littering, and taking your shit home with you, especially your tents and sleeping bags.
https://www.glastonburyfestivals.co.uk/information/green-glastonbury/our-green-policies/
b; I expect they do make enough money to employ people to clear up afterwards - so why do they get 'volunteers' to help do it, and only give them entry to the festival by way of payment?
c; It's a working farm yes, except of course the area of the festival for the month before and after the event, while they set it up and then dismantle it all, and then they can't let livestock onto the area until it has been thoroughly cleared of all debris and anything likely to be toxic/dangerous.
I don't give a flying fuck for the environment, but I don't go out of my way to be deliberately polluting either.
I just get on with my life as sensibly as possibly without bothering others or trying to provoke an argument for the sake of it.
What I have a problem with really are the self-contradictory hypocrites and sanctimonious pricks and celebs who want to lecture the general public over how they should be saving the planet etc whilst themselves driving gas-guzzling motors and flying everywhere, usually in private jets.
Those people are not as environmentally friendly as promised, but they like to try and convince you that they are.