This is certainly censorship but the "they think we're stupid" explanation is not at all appropriate. UDE does not control what Konami does and I would be quite surprised if they had a desire to influence them in these types of decisions. Konami has their own view of this issue, cards that are fine in Japan under their own views of what is and is not appropriate are based on Takahashi's Japanese view on what material is suitable. Japan is neither better nor worse than the U.S. in what it does and does not allow but the directions of censorship and appropriate content are somewhat different. Are you going to insult every American company who has modified their products for the Japanese market as well?
Do they go overboard with these edits? Absolutely. But the edits are an attempt to keep some very reactionary groups from having a problem with the product (and if you don't think there is some sense in this you truly haven't watched the absurdity level of the Christian Right Wing and where they have previously seen the signs of devil worship, witchcraft, etc.)
The better question to ask is who chooses what to edit and why are those decisions made so poorly. Some cards are edited that couldn't possibly have been considered offensive or set off any flags (The Unhappy Girl), while others with content that is standardly edited come through without being touched (Maiden of the Aqua).