If you're looking for a mostly-rational way to look at whether, when and how much to give to charity, I'll throw out some thoughts.
1.
Give to charities because it is important to you and part of your ethos.
MMM is about frugality-- which is spending your money efficiently on what is important to you in life, and giving up unnecessary things. It's not about stinginess-- which is giving up important things in life for money. If FIRE as soon as possible were the only goal, we should all give up our homes, adopt out our kids, move into the cheapest roommate situations possible, and eat only the necessary to keep alive. No entertainment. Cheat and steal whenever safely possible. But no, this is not the way of happiness. Drop the unnecessary, but don't let go of the essentials-- such as family, enjoyment of life, health, kindness, and honor.
2.
Give to charities as an investment in the future and world around you. MMM takes the long view. Care of the earth and our society is beneficial to the stability necessary to make a long, happy, early retirement. Also, better to invest in charity earlier than later.
3.
Choose your charities as carefully as you would an investment vehicle. You have limited time and resources-- make them count. This is a very tricky piece of optimization and will need occasional recalibration. Will $10 donated directly to a homeless family be as well spent as $10 donated to a food bank? How much money or time should you donate?
It's a very personal calculation. We all have financial goals on different timelines that require a certain level of saving. Once we have removed our essential payments (housing, food, taxes, utilities) and our savings payments, we have some money left over. Also, once we have done everything we need to for the day, we have some time left over. These excesses we divide between investment for the future, recreation and charity.
If you are not able to give to charity without staying in debt or extending your timeline, and you can't bear to extend your timeline for some reason, your recreational/charity budget will be very small. But it probably won't be zero unless you can live with yourself as a human being that way. Basically, if you can spend $5 on something stupid like a latte, you can donate that much too.
But perhaps you can give some time to charity because few people can work all their waking hours. The time you donate would be best spent using your skill set, unless you need a break from your expertise, in which case it could be seen as part recreation or even training.
How about investment vs. charity? If you are certain that you
will eventually donate that money, and not end up keeping all the money for yourself... and that the investment gain is greater than loss to the charity by not receiving the money earlier... okay, I guess. But when I am tempted by selfishness to withhold charity, I often think of the following poem.
https://www.poetrynook.com/poem/legend-northlandChoosing the most efficient use of charity dollars is not easy to do objectively. Sites like Guidestar and Charity Navigator help, but can be gamed. As for what sector to choose, it's difficult. I used to believe that education and the environment were most important, but lately I've come to think that income inequality plays a great role too in all the striving that causes people to over-consume. That's off-topic, but at any rate it was driving me crazy until I decided the best thing is not to be paralyzed, but for everybody to work as hard as they can on the essentials and all the shared goals, and improve when we see an improvement to be made.