[yummyfajitas]

Your specific example doesn't read to me like subterfuge at all. It looks to me like an informal discussion which may lead to a purchase of securities. After you say "yes" via email, we will probably construct an actual contract specifying details.

The disclaimer makes certain that both you and I realize this isn't an offer, just a conversation.

You might get into trouble if you routinely engaged in securities transactions via email with such a disclaimer. But if you handle all actual trades with a legalistic form containing no disclaimer, and informal conversations in email with a disclaimer, the disclaimer is likely to hold up in court.