We can't rule out the possibility, though, that Seuss was just making a more general statement about equality. After all, the mantra, "a person's a person, no matter how small" is a good one to apply to just about any situation of inequality.
P.S. Lots of people interpret that mantra as a pro-life message, but the Seuss family was a supporter of Planned Parenthood and Seuss himself apparently threated to sue some of the groups that adopted this phrase for their own purposes (source). So we're not so sure.