Phil's:

You shouldn't take it as an axiom that the SIAI is the most-beneficial charity in the world. You imply that anyone who thinks otherwise is irrational.

...was questioning XiXiDu's:

If everyone was to take Landsburg's argument seriously, which would imply that all humans were rational, then everyone would solely donate to the SIAI.

...but it isn't clear that the SIAI is the best charity in the world!!! They are in an interesting space - but maybe they are attacking the problem all wrong, lacking in the required skills, occupying the niche of better players - or failing in other ways.

XiXiDu justified making this highly-dubious claim by saying he was trying to avoid getting down-voted - and so wrote something which made his post "sound more agreeable".