the ingredients. I wonder if the pectin interferes with the cultures making the milk congeal correctly.
You are correct in that the pectin will interfere. Do not use low fat or fat free yogurt.
It's worthwhile noting that you can use low fat or nonfat yogurt as starter, but most of the varieties found in grocery stores have all kinds of thickeners and stabilizers that might interfere with the process. Low fat is not the problem. I always make my yogurt with skim milk and it comes out perfectly set every time.
I have used Danon before with undesirable results. The pectin in your starter will result in a slimy home-made yogurt. I recommend using a brand that does not contain gelatin or pectin. I have had good results with Fage Greek yogurt. Lifeway brand Kefir drink works well also. I sometimes use Lifeway probiotic Kefir with the added benefit of the additional bacteria that comes with it.
As long as it has live and active yogurt cultures, it should work as a starter. The pectin is there to add to the texture and consistency, so I can't see that it would interfere with the yogurt cultures work. I've made yogurt with all different kinds of plain yogurt. The only thing I ever checked for was the live cultures.
I would try to find a better quality yogurt than Dannon's. Try a locally produced yogurt, perhaps from a farmer's market or dairy. The bacteria should be fresher and rarin' to go. Before we were able to buy yogurt made close to home, I used Dannon's. No way now, knowing how good real yogurts can taste, would I use the corporate yogurt today.
Interesting what he says about speciality yogurts. I have had good luck with them.