The quote doesn't say that whatever is legal is moral. It makes a specific judgement that arranging your affairs to keep taxes as low as possible is not immoral

The quote doesn't say that whatever is legal is moral. It makes a specific judgement that arranging your affairs to keep taxes as low as possible is not immoral, and it points out that everybody does this, rich and poor, corporations and people alike, and that demanding others pay more than their required amount is hypocritical and sanctimonious.