I have some sympathy for this point of view, especially having regard to the situation in many countries where there is no heraldic authority (such as the College of Arms in England or Lord Lyon's office in Scotland), and perhaps not even a quasi-official register of heraldry (such as can be found in Sweden).I don't see why anyone should scoff at the assumption of arms especially when one has no option as is the case in the United States.
My concern is that those who are not heraldry adepts (nerds, geeks or whatever) may take the notion that it is acceptable to assume arms to mean that they may assume the arms of someone with the same surname, or arms that they like the look of. This is never OK.
In some places it is acceptable to use the arms of one's extended family. But, for example, I with the surname Green would be quite wrong to usurp the arms of a Swedish person of the same surname, since it is simply a coincidence that the two names are spelt the same. There is no family connection. Similarly a Swedish Green would be wrong to assume my arms.
As for assuming arms that one likes the look of, to me that is plain silly. If you lack the ability to design your own unique arms (which may incorporate ideas from arms that you admire), then there are many people who can help you, either for a fee or gratis.
Arms are intended to identify people. Using someone else's arms may not be identity theft in the same way as stealing someone's identity for the purpose of internet or banking fraud, but it is still a form of theft.