Case of causing someone to sin?

Question

Are there any sources that the following case would constitute causing others to sin?

A person addressed a nonreligous Jew about keeping kosher, and tried to make him keep kosher. The non religious Jew said he doesn’t keep kosher but does not eat meat and cheese. The religious Jew replied “You might as well eat meat and cheese if you're eating nonkosher.” The non religious one took this advice and started eating meat and cheese.

Does this mean that the religious Jew caused the nonreligious one to sin, and will receive punishment every time the latter eats meat and cheese?

Answer 1

There is a prohibition against inciting a person to sin, which is referred to as מסית לדבר עבירה.

Source: See Iggros Moshe (OC 1:99) that even though Beis Din only punishes a person who incites to idolatry, the prohibition against "inciting", applies to all sins, and in any case he is punished by the laws of heaven.

See also ibid. (OC 2:7) for further discussion of this point.

The critical question is whether the relevant statement by the religious Jew constitutes "incitement to sin".

Answer 2

He didn't actually cause anyone to sin.

The prohibition of eating Meat & Milk together applies only to Kosher animals*, and presumably, this is what the religious Jew meant. There would be no prohibition [of cooking/eating Meat & Milk together] if the food was from non-Kosher species.

*(This excludes only species that are not Kosher, not Kosher species which died without a valid Shechita. Neveila & Treifa are subject to Basar veChalav.)