oomiss1105, wearing non-tsniusdic clothing, besides being a lav, causes yetser horah for gilui arayos R’L — so, in a way, it is even worse than eating meat of a non-kosher animal.
chesedname, a baal tshuva is obligated to keep all the mitsvos just as any other Jew. The only p’tur is being a tinok shenishba (someone who was indoctrinared with a non-Torah worldview since childhood and never had a chance to know better). Someone, who realizes that Torah is emes, has no p’tur.