What makes you think SWA is such a threat out of HOU?
Forgot to answer your question. The reason is, ultimately, you have no problem flying out of IAH. In fact, you probably plan to. It's like Chase readily admits on page 1 of this thread. SWA is going to end up going to DFW. Even with all the decades of WA drama and consternation, SWA will end up going to DFW. Houston doesn't have to wonder what your plan is. You intend to skirmish from a safe distance with the IAH carriers, assail IAH as ridiculously expensive, and ultimately wreck the airport financially and contribute to the bankruptsy of the predominant carrier. Then move in when you can get the whole thing for cents on the dollar.