A former rebbe whom I highly respect advised me not to eat any food product that has more than one kosher certification on it. His thinking was that in principle, the concepts of kashrut and achdut - unity or community - moust go together. In other words, certifying a product as being kosher is a form of allowing a community, i.e., the consumer, teh halchic "permission" to eat the product.
His claim is that if there is more than one mashgiach (supervision) on a product, either the 1st mashgiach wasn't competent enough or "certain" of the kashrut, so he had to ask a second person (or 3rd), or that even if the 1st mashgiach completed the kashrut job and said something was kosher, some other mashgiach didn't sufficiently trust the 1st person, for whatever reason, and had to supervise it himself.
He also claims, that in terms of the consumer, the multiple certifications would make a "novice" consumer (by "novice" I mean someone who is just looking for a kosher product an doesn't understand the politics or other reasons involved behind the kashrut process) question what's going on. Additionally, the rebbe claims that it may be a form of Chillul Hashem, esp. to non-Jews who may conclude the same thing - that Jews can't agre.
Now, I'm confused, myself, here. I attend weddings where the almost all of the deserts come from Chantilly, who makes delicious pastries (so many people tell me that, and they look gorgeous), but because Chantilly's products have 4 or 5 kosher symbols, I can't enjoy the Vienese table.
Is there any validity to my rebbe's claims? Does having multiple symbols weaken the reliability of the kashrut of that item?