Interesting, I came to the same conclusion, making my dangerous robot look dangerous on purpose to keep people away from it. Are there actually written rules on this policy somewhere?
This is one reason I oppose rounded corners in GUIs. A computer is a power tool for information manipulation. Power tools are always dangerous. When you can cause massive data loss or worse with a single mistake, it shouldn't look "friendly", any more than a firearm or a table saw should look friendly.