But let us see what those statements of his are which follow next in these words: “Nay, we see, indeed, that even those individuals, who in the market-places perform the most disgraceful tricks, and who gather crowds around them, would never approach an assembly of wise men, nor dare to exhibit their arts among them; but wherever they see young men, and a mob of slaves, and a gathering of unintelligent persons, there they thrust themselves in, and show themselves off.” Observe, now, how he slanders us in these words, comparing us to those who in the market-places perform the most disreputable tricks, and gather crowds around them!
What disreputable tricks, pray, do we perform? Or what is there in our conduct that resembles theirs, seeing that by means of readings, and explanations of the things read, we lead men to the worship of the God of the universe, and to the cognate virtues, and turn them away from contemning Deity, and from all things contrary to right reason? Philosophers verily would wish to collect together such hearers of their discourses as exhort men to virtue—a practice which certain of the Cynics especially have followed, who converse publicly with those whom they happen to meet.
Will they maintain, then, that these who do not gather together persons who are considered to have been educated, but who invite and assemble hearers from the public street, resemble those who in the market-places perform the most disreputable tricks, and gather crowds around them? Neither Celsus, however, nor any one who holds the same opinions, will blame those who, agreeably to what they regard as a feeling of philanthropy, address their arguments to the ignorant populace.
Source: Against Celsus (New Advent)