Leviyitz and Joseph,
Rav Kook, in a letter to a rav whose sons became communists, compared the spirit of the times to an evil seductress (see Sanhedrin 26b with Tosafot d”h hechashud). I heard that Rav Scheinberg also said that today the forces of tuma are so strong that even a yeshiva bachur who goes OTD can be considered a tinok shenishba.
Rav Ovadia ruled that a Jew who does not keep Shabbat does not cause wine to be prohibited (Yabia Omer 1 YD 1).
Rav Asher Weiss also says that today a Jew who does not keep Shabbat is not necessarily considered to be like a goy. That would only be if he disconnects from the Jewish people (Rav Weiss said if he marries out).