I think the tragedy of the modern world is that the average member of the public wants music for free but won't bat an eyelid overpaying for a coffee. When it comes to charity shows and the overused word of "exposure", it is interesting that the band is the first thing to be eliminated from being paid. People are not showing up to watch the person on the door or the person serving them.
Throughout the 90s, I don't think I did any paid gigs. It was either a free gig or the minimal payment went into the band. Fast forward to now and my duo has done a few paid shows - all our money goes back into the band. We've also done freebies and open mic. I need to see us getting something, be it genuine exposure or just the opportunity to play a decent stage.
I think for bands who write their own music, the standards shift. I wouldn't do a covers or tribute show for free because I would expect it to be of a standard where we got paid. Playing in my originals duo, it is more niche so I am alive to venues struggling. That said, I think many promoters could sometimes try harder. A couple of drinks and a meal isn't costing pub prices and things like collections for the band, covering fuel etc should all be used more widely. Musicians and their friends often spend the evening in the venue paying full price for drinks etc. I'm nearly 12 months alcohol free and the costs still build.
Ultimately though, I would never criticise any band member for their choice to either purely play for fun or only demand paid shows. Your band, your rules.