The history of opera exactly coincides with the history of people complaining about opera. But few can claim a better-heeded cavil than Francesco Algarotti, whose “Essay on the Opera” inspired one of the genre’s most indelible masterpieces. Armed with Algarotti’s strictures, composer Christoph Willibald Gluck and librettist Raniero Calzabigi produced “Orfeo ed Euridice,” their 1760s avant-garde translation of the mythological tale of the musician who sings his way into hell to retrieve his deceased wife, performed on Friday and Saturday by Boston Baroque and conductor Martin Pearlman.