I just read through this thread, and like swanic, I'm going to give my most thoughtful response on what happened to you and why you received such a harsh backlash. I think as a society, we've become more and more inclined to lay blame when something unexpected happens to us, even when we are diligently following what we perceive to be the rules or the official instructions given to us. After all, if something wrong happened, and I did exactly what was said, how could it possibly be my fault? It must be someone else's fault. There are no accidents, just cause and effect.
As I read through the product description of McKee's Coating Prep, the description is very clear that it is a paint prep solution. I rightly can infer that it is designed to be used on paint, but I cannot infer that it can be used anywhere else. The description states that it is for paint, and it nowhere implies that it can be used elsewhere. That's just my take of the website description. I don't have a bottle of this stuff, so I don't know what the label on the bottle states. Maybe it states it can be used on multiple surfaces; I don't know.
All I can do is conclude that the coating prep is made for paint. I assume that the paint prep either is OK for other surfaces (plastic, vinyl or leather) or that it is untested on those surfaces or that it might possibly be inappropriate for those other surfaces. Since McKee's offers no information, I can't make a conclusion and I, therefore, must assume (to be safe) that I shouldn't get it on those surfaces -- unless I want to specifically test the reaction. (I stained my white lab coat this morning with some Au Bon Pain coffee -- I didn't read in the description on the coffee cup or on the menu board that it could stain my white coat.)
So, I think there was some assumption on your part (or some carelessness) if the prep solution spread to your plastics.
Take another look at your lead post; I think even you can see that it is somewhat accusatory and ill-deserved:
You used all caps -- that's an interwebs no-no when having an online debate. You used the phrase "what the hell." Not terribly offensive, but it steps up the level of animosity for sure and suggests that McKee's was intentional or nefarious. You stated that you were "forced" to use the degreaser -- as if you were unwillingly put under direct pressure to do additional work for the nefarious McKee's.
I think a better way of starting off this post would have been to say something like this:
"I used McKee's prep polish the other day. It was about a year old, so on the edge of its lifespan. I noticed that it stained some of my plastics and I had to use a super degreaser and a lot of elbow grease to get it out. Has anyone else experienced this with McKee's prep polish? I realize it's for paint, but I unfortunately got it on the trim and was super bummed. Does anyone know if X,Y or Z products would be more effective at getting out these stains?" Title didn't help either.
The thread might have had a different tone...