I would say most laypeople would agree that using applied mathematics to hedge investments and reduce risk is okay. Most would probably also say that creating overly technical mechanism to obfuscate what is really going on would not be acceptable. I think this is why people cringe at the prospect of more and more derivative financial products being 'engineered' to create value.
I personally say it gets gross from the standpoint that it is almost entirely a field of contrived rules of convenience. In other words, the 'system' is entirely human-created which comes with all the shenanigans humans bring to the table. This is in contrast to traditional engineering disciplines that are generally rooted in some sort of physics. A mechanical engineer can improve their understanding of reality, but cannot wave a magic wand and make different a different reality for their system to operate within.