I don't think a "bad supplier" list is necessary. It just seems really negative. Some people may have had bad experiences with generally good suppliers, and vice versa. Making a list paints suppliers with a broad brush that may not be entirely accurate.
If someone is concerned about a certain supplier, I think they should post a forum topic asking about other's experiences and decide for themselves. Or do an internet search for reviews. You know, do their due diligence.
I agree with MrsMuscipula. I do think it's important to consider that a single, bad experience does not define a store - even multiple bad experiences could be indicative of an issue we cannot see, such as troubles within the supplier's company. (I'm not trying to make excuses here, it is something to keep in mind however.) It's absolutely important to consider both positive and negative experiences, which is why I encourage reviews on the list of online suppliers, that gives people an opportunity to share all their experiences and make an informed decision based on those experiences.
So while I don't dispute the importance of negative reviews, constructive feedback can help a company grow, I feel that a list of companies dubbed as "bad" could do more harm than good in the long run; this is not because negative reviews are bad, certainly not, but rather because I strongly feel both sides of the story need to be considered. Even if a single positive review in a sea of negative ones won't convince you to buy from that company, it at least gives you an opportunity to see things from both angles.