I believe the professor was wrong on at least one fundamental level - his application of the whoredom discussion in the second chapter of Jacob to petting and kissing. However, I believe he was correct in his statement that the Lord doesn't care if fornication is homo- or hetero-sexual -- that the sin is the same. Let me address that point from two angles.
First, petting and kissing (of any kind) are not condemned in any of the canonized scriptures of which I am aware. Those records condemn the categories of sexual activity known as fornication and adultery. This broad categorization includes pre-marital and extra-marital sexual activity - or activity of a sexual nature.
We do have a written prohibition against these same types of activities in what we accept as the words of modern prophets and apostles - the "For Strength of Youth" pamphlet. Among other things, it says to abstain from petting, "passionate kissing" and any other activity that arouses sexual desire. It doesn't distinguish between hetero- and homo-sexual activity; it prohibits both equally.
In this case, I see a very clear and simple "why." Petting, passionate kissing (NOT kissing, but "passionate" kissing) and other similar activities (including, in my mind, anything that simulates intercourse) arouse sexual desire. Sexual desire can be very hard to control once initiated. Hence, the counsel to avoid any activity that might logically lead to a losing battle with escalating desire for more stimulating activity. "You can't finish what you don't start" is a truism.
I see the smoking and drinking prohibitions in the Word of Wisdom in exactly the same light. If I make it a scientific issue, I lose. There is much evidence that alcohol used in moderation has positive results for many people. I just read this week an article that described the positive aspects of caffeine consumption - one of the richest sources of antioxidants. Yet we are asked to abstain. Why?
Because of evil designs of conspiring men. (Which applies perfectly to those who seek to stimulate sexual desire, as well.) These substances are addictive, and the consequences of over-indulgence can be disastrous -- especially for a drunken woman. The article I mentioned in the last paragraph skipped blithely over a statement that heavy coffee drinkers are much more likely to be heavy users of alcohol and cigarettes. It is impossible for each individual to know, with certainty, what his or her limit is prior to reaching it. Because it is not always easy to know those who are weak and prone to misuse, the prohibition has been "adapted to the weakest of the weak who are and can be called saints."
In other words, if I am strong and not likely to have a problem, then it should be easy for me to abstain; if I have a problem abstaining and find myself fighting the restriction, then I probably am weak in that area and benefit from the prohibition more than others might. (That, in and of itself, is a fascinating concept - that the areas where I need repentance and outside guidance the most are exactly the areas where I want it the least and work to justify my rejection of it the most. Often our biggest weaknesses are most apparent by our claims that we are strong enough to not need outside prohibition or counsel.)
As an additional rant, I have a HUGE problem with those who rail against homosexual activity but are quick to forgive and excuse heterosexual fornication and adultery. I have always said that punishing homosexual activity in any way without doing the same thing for heterosexual fornication and adultery is hypocritical and narrow-minded. That's why, although I oppose redefining marriage to include homosexual relationships, I have no problem, within the context of our heterosexually lenient society, with creating a legally recognized way to allow homosexual partners to live in a committed relationship without fear of legal punishment. Again, the alternative is hypocrisy.