We have laws like this for computer hackers. No-one ever defends themselves by saying "everything I did was enabled by the poorly designed system, therefore I am not a criminal". Why not for the financial system?
People charged with hacking defend themselves this way all the time. And other people defend them in the same terms.
Recently a guy was charged for accessing public URLs. Sure, they were specifically made available to the public, but the public wasn't supposed to look at them.
...no evidence was advanced at trial that the account slurper ever breached any password gate or other code-based barrier. The account slurper simply accessed the publicly facing portion of the login screen and scraped information that AT&T unintentionally published. [0]
[0] http://cdn.arstechnica.net/wp-content/uploads/2014/04/weevru...
For traders, we don't have all-encompassing laws covering tax avoidance. Plus, traders have money for hiring professional for finding loopholes.
That's the difference.
Because the CFAA is pretty universally hated and makes for bad outcomes.
This is a pretty common argument, actually, when it comes to questions of "allowed" API access.
*good as being defined as likely a net positive value on society similarly bad as being defined as a net negative for society