Thank you for sharing your thoughts. There is a lot to respond to, so I’ll address only some concerns.
You state “what if the art museum inspires others to give?”. It’s worth contemplating this, but what is your honest opinion: how many millions of people would have to visit a museum before one of them is inspired to give more to charity than s/he would otherwise give?
You state “what if those people who have newly restored sight are still going to live a life below the poverty line, albeit with sight”. Do you sincerely think that giving someone the ability to see again is pointless just because their life is not as high in quality as that of an average citizen of a developed nation? Needless to say I’m puzzled why you don’t think that a person with sight (at the very least!) has a much higher chance of finding work that can improve their financial situation.
About the kidney donation, you say “But what if the person your kidney goes to is a non-philanthropic, rather terrible human being who only has a few years left to live anyway?” Of course that’s a possibility; would your policy then be that we ought to prevent all kidney donations from strangers to strangers? Do you think that would be a better world to live in?
You then say “What if you make so much money that even at such a low risk, the difference in expected donations you could make pre- & post- surgery is in the millions?” Well, the person who wants to maximize the amount of good in the world, in that scenario, abstains from giving their kidney and instead keeps donating the millions that s/he is earning.
I can say more if you’re interested in engaging in a conversation.
No matter what, I salute you for starting (and continuing to engage in) a discussion about a topic that is clearly so important.