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.

Yes, I agree. But let's not slander Learned Hand by attributing to him the intentions of those who quote him. In fact, compared to some more recent justices, I am confident that he would have filed outraged dissenting opinions in recent cases where the law made by representatives was set aside and, in some cases, new law was imposed from the bench.