You shall make no covenant with them and their gods. They shall not remain in your land, lest they cause you to sin against Me; for you will serve their gods - and it will prove a snare to you.
I was recently asked by someone I very much respect to address "the" question. So I started to write the answer in a post... about five times without any luck. The "Why does a 20-something join a Reform Congregation" question.