People are all to willing to push the boundary, and try and find "justifications" under a Catholic banner for immoral behaviour.
We are to be chaste in our vocations, whether marriage, single, dating or religious life. Just as sodomy is wrong between the married couple, and an offense against chastity, "French kissing" and its varients are serious crimes against our purity for the unmarried. Not only that, they open the door to temptation, and can result in the sin of scandal if someone else was to witness such behaviours.
Of course, we carry a nature wounded by sin, people are always trying to legalise their way out of sin. Just look at the people on this forum who dont accept the Church's teaching on fornication. The whole "Well, Jesus understands, we love each other and are committed to each other, after all. AND we're getting married in six years once his promotion goes through and I've finished my studies" is heard all to often from both Christian and non-Christian alike.