Here’s what the Lubavitcher Rebbe said in 5751, according to the Chabad.org discussion on tinok shenishba
“However when one stresses and emphasizes the disadvantage of those who are non-observant, also adding warnings of punishment and retribution, Heaven forbid, not only is this not the way to strengthen the keeping of Torah and mitzvos, rather it weakens observance and distances the non-observant from doing teshuvah.”