I just think the “black Arrow” story could be conveyed just as brilliantly without all the “colourful language”. It would still be a brilliant book for the freedom movement and might reach people who don’t want to wade through a sea of silly, pointless, obscenities.
I think you must live in a sheltered world, dear. That IS how a great many people do talk out in the real world, at least in the US. I've heard it - increasingly -for the last 20 years or so. That may well not be how they talk in your area or country, but they do here, and especially in the big cities. Whether or not that is good, bad, evil or just stupid is quite beside the point, since none of us can do a damned thing about it except watch our own mouth - and vanishingly, that of our children.
I don't use that language at all myself, but I don't waste much energy worrying about those who do.
And of course he could have avoided all or most of it if he'd chosen to do so. But he CHOSE to use the language of the streets - as HE sees and hears it. That is the power of freedom, in literature as in anything else. His writing, his story, his book, his choice of language and everything else. He also bears the risk of not finding an appreciative market for all that if enough people don't like it.
You have the absolute freedom to read it or not - or just parts of it - just as it suits you.