I think the argument is that this a scheme clearly setup to flout the law. If those haikus kept going by a business exec until an associate should sell the company's stock, would that be an acceptable way of insider trading?
At the same time, companies should not be forced to try and circumvent the law with cute tricks. Preventing companies from informing their users/customers that their privacy has been breached by a 3-letter-agency should be illegal.
We shouldn't be arguing about the legality of canaries, we should be arguing about the legality of gag orders. Arguing pro canaries is fighting a losing battle; it's fighting the symptoms instead of the cause.
In the example of insider trading, it was NEVER legal for you to give inside information. So stopping your Haiku is legal, but the discussion when you agreed "sell your stock when my Haiku ends" was not.