The issue is the word 'charity' not 'fair price'.Only problem is, there is no universal way to determine what is fair price. It's completely subjective and depends on ratio of price and value you get out of product.
Best way would probably be - price with which both buyer and seller are reasonably satisfied.
Paying a fair price for something isn't 'charity'.
Even if I can be convinced of that -- I have no opinion on this currently -- it won't affect my buying pattern. I trade money for a product based on the merit on the product. If I think it is going to bring me 20 € of value, I won't buy it 50 € even if it would allow authors to be paid better. I mean, I can see me doing that when buying coffee out of charity for East-African coffee planters (while thinking it's probably middlemen that benefit the most), but I don't feel charity is a factor when paying workforce in a country with similar or higher wealth level than mine. I am pretty sure I am not the only customer to think like that.
I think it can be a useful or valid excuse, because art is usually a fixed price.
No, it isn't, but paying for something that you don't need for a price you're not otherwise willing to pay, is charity.Paying a fair price for something isn't 'charity'.
I know it's worse for SF2e then it's for PF2e Remastered from two years ago, which in turn is worse then the D&D 5e physical sales. While some still prefer physical books, some need physical books because for some reason they can't comfortably read books on a digital medium. But over time more and more people will prefer digital over physical, making physcial products even more expensive...

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.