AAQ, I don’t know who you consider choshuv, but normative halacha does not exposure to apikorsus for average or even above average individuals leshem da ma lehashiv. Rav moshe writes this regarding reading the new testament; he allowed rav avigdor miller (who asked) because he was an actual gadol batorah who had already finished shas many times. The proper fulfillment of da ma lehashiv can be done through kosher sources which were designed to counter those ideologies; rav avigdor Miller’s seforim are one such source, as are the chovos halevavos, emunos vedeos, kuzari and moreh nevuchim. Hearing about it from a supportive, positive source such as an immersive college course is a whole different level.
There were likewise “choshuv” voices which allowed chilul shabbos for work, because of cliched applications of maxims of chazal such as “asei shabatcha chol”. These were actual rabbis of towns in Europe, who were also maskilim. The lines weren’t as clear cut as they are nowadays. Nowadays one can easily know if someone is divergent from mesorah in the way that they dress – take a look at pictures of shlomo yehudah rappaport (he liked to be called “shir”). He was the rov of… Prague? Either that or another major city. He was a complete maskil, but he looked indistinguishable from the chasam sofer in his outward appearance.