I think separating the idea of legality and ethics would be helpful. Additionally, don't try to apply this to a single product as that can go down a rabbit hole of opinion way to quickly.
So lets look at the idea of a straw purchase with out the confusing ideals of a specific product attached to it. First thing I would ask is about the legal status. A simple google search tells us if any commodity or product has a law, regulation, or rule governing it. Honestly, the legality of the situation really is that simple. There are some specific items in this world that are heavily regulated and/or controlled, otherwise it's open season as far as the legal aspect. If someone is considering this route for what they believe is a valid reason on a regulated item or commodity then they should seek professional legal council and act accordingly.
Now as for ethics, that can be a far trickier question. Who is to judge what is "ethical" in a legal transaction? I would say it's civil case law here in the US, in which case that's a fairly broad and open avenue to operate on. As stated above by others, this is a commonly used process for a multitude of reasons. The reality is, as long as no one is being defrauded or otherwise disenfranchised in the transaction ethics doesn't really come into play. I believe we have a right to remain anonymous if we choose and a so called straw purchase is a perfectly valid way to do that. So long as there is no contractual or legal obligation saying otherwise, engaging in a straw purchase or using a broker or a buying agent are one in the same and are perfectly fine.