"Well, all I can say is that neither of those problems occur in my pro's teaching. I don't know on what basis you generalize your statement to all or most pros who teach pro-am students."

The statement was not a generally one, but was offered to refute your unfounded claim that dancing with a pro is somehow protection against developing bad habits. Dancing with a pro for exam purposes would be one thing - but toss in competition pressure (in a division where appearence is everything and technique often lax) and the pragmatic result may deviate far from focus on proper habits.

"Nor does being an amateur couple preclude the lady from pressing her hips against her partner or creating shape incorrectly. Why would it?"

The simple reason is that professional men have a reserve of strenght and ability to draw on in compensating for a student's bad habits, which few amateur men share. A pro-am partnership is not an equal one, but usually one optomized to make the most short term use of the stronger partner. Unless the student is not attempting competition but focused on improving her dancing as its own goal - that is the time when the alleged advantages of pro-am may be real.

"After all, except for the very top coaches who only coach couples (my pro and I take periodic coaching from such a person), it's usually the same pros coaching the am couple that also teach pro-ams."

Sit and watch for a few hours and you'll see how the two types of couples are getting very different coaching from the same teacher. The demands of competition are different, the assets the couples bring are different, and as a result the type of dancing that results is different. BTW, it's not uncommon to see amateur couples trying to dance with pro-am styling - usually they are trained in isolation from established amateur programs, and do not go far once they meet real competition.

"What no one has explained is why the ams seem to need to insult pro-ams. I rarely see the reverse".
Well, this comment is so far from the truth I can't even detail all the ways that I have seen pro-ams insult ams.
I will give one example. One that came from someone who I thought was a friend. My husband and I competed in the Championship Level of American Rhythm and we were pretty proud of our accomplishments. Having started out in bronze and progressed all the way to the top, together, with out the benefit of any real extensive pro/am dancing was, we felt a huge accomplishment. Later, I found out was always very jealous of my having a partner all the time while she had to travel to dance with her new pro partner. She would exbibit this with little quips like "now you know how I feel" or "now you know what it is like for me". This happened if my husband was traveling or for some reason was not dancing at that moment with me. It blew up after she did well in a pro/am comp with her new pro(who is the #3 most demanded pro in the country and also our coach). She proceeded to tell me, my partner and a friend of ours that am/am dancing was not as competitive and therefore not really a challenge and all the work we put into our dancing did not count for anything.
She also said "I am dancing with E.A. now and that makes me a great dancer because he won't dance with just anybody". Needless to say, her lack of respect ruined my regard for her. I was always supportive and sympathetic with her struggles to find a good pro/am partner, so her back stabbing of am/am dancing gave me a peek into her true personality and her sense of superiority. Which she now does not even attempt to cover up anymore.
So, take a good look around you. If the insults go one way, they also go the other. It is never a one way street.

OK, I'm done. I've made the alternate arguments for anyone who wants to read them. All I'm trying to say is:

1) there are advantages and disadvantages to both modes of competing. Which is best for you depends on your circumstances and dancing goals.

2) it's dangerous to generalize. There are bad teachers, misguided students, and just plain obnoxious people in every variety of dance. There are also excellent instructors, dedicated students, and great people in every variety of dance. Look for the latter and avoid the former, in your dance studio and online.

I totally agree with your two points, Ellen. Thank you for the concise summary.

I danced in both Pro/Am and Amateur partnerships for over 8 years, so I think I have a good picture of both sides of the equation. Both have their advantages, both have their drawbacks, and both depend upon the quality of the instuction and the quality and dedication of the people being instructed.