You know Numbers in English Grammar. Has two types Singular form and Plural form. Right? It has to be like that. In the song Human by the band the Killers why does the vocalist sing Are we Human or Are we dancer without plural s or the plural form of dancers (Noun - Parts of Speech again English Grammar)? Because we is first person plural and with that plural form of Noun goes. Like dancers in this case. Why is this intentional grammatical mistake? It's a well known, famous and hit song. It cannot be intentional grammatical mistake.
There must be an underlying reason for it. I wonder what is that reason?