I think this APC system is terrible -- it's enshrining the principle that publication in ACM venues is only open to researchers in institutions that are rich enough to cover the publication cost (or be recognized as lower-middle income). Of course this is already mostly the case, and it is already the case with conferences and their expensive registration fees; but we will stand no chance of ever improving on that front if journal article authors get charged >$1000.

Compare this to diamond OA journals (e.g., in my field, https://theoretics.episciences.org/ or https://lmcs.episciences.org/) where reading and publishing is free for everyone. Of course, the people publishing in these journals are mostly academics from wealthy universities, but I think it's important that other authors can submit and publish there too.