I don't think the ad is exactly glorifying Mao, it's more using him as a contrast, pointing out he created the "least diverse collection of books" while the library allows free expression.
Another ad in the series that came under fire uses J. Edgar Hoover and his spying on libraries.
I don't think you can compare the evil of Mao to J. Edgar Hoover. J. Edgar Hoover did not kill millions of people.
This ad is stupid. It would definitely deter me from contributing to the library in any way, and will probably undermine public support.
They were trying to be creative, but I think they went a little too far. The ad is not sufficiently critical of Mao.