Laudator Temporis Acti

Basil Lanneau Gildersleeve, "Brief Mention," American Journal of Philology 32.2 (1911) 230-242 (at 238):

There is no question of the existence of the gods in Aristophanes. Euripides is skeptical. Euripides' acid is the acid that eats up the molten image. The acid of Aristophanes is a mild solution that merely stings and prickles, but does not destroy. Orthodoxy covered a multitude of sins then as it does now. Aristophanes was orthodox, Euripides was a rationalist, if one dare use so modern an expression. Religion being an affair of state, the Greeks were not exacting. νομίζειν θεούς is not a matter of conscientious ground of action, as Mr. Neil says in his note on the Equites, 515. That is one of those obiter dicta that are always bobbing up in commentaries. νομός is convention. Accept the gods the state provides and all is well. The trouble with the Christians under the Roman Empire was that they were so absurdly uncompromising, that they followed the direction μὴ συσχηματίζεσθε so closely. No sensible Roman could understand their attitude. A pinch of incense, a kiss of the hand would answer? What reasonable human being would object to meats offered to idols? ἱερεῖα after all is only butcher's meat.

Modern scholars are skeptical about Euripides' supposed religious skepticism. See, e.g., Jon D. Mikalson, Honor Thy Gods: Popular Religion in Greek Tragedy (Chapel Hill: University of North Carolina Press, 1991), esp. chapter 6, and Mary Lefkowitz, Euripides and the Gods (Oxford: Oxford University Press, 2016).