Many seem to use points to speculatively purchase trips when their travel plans are not firm. Hopefully everyone is responsible enough to cancel these reservations well in advance when it becomes apparent that they will not be used - I wouldn't really mind if SWA extracted a penalty for no shows - just to preserve the flexibility for the rest of us who do cancel unused flights in a timely manner.
I often wonder whether a flight purchased on points 4 months out and then canceled two weeks out will go back into inventory at the same low price as originally purchased. Its doubtful, most revenue management programs are tied to load factor and length of time prior to the actual travel date. Most likely flights purchased "early" at low point prices will, after being canceled, appear back in the remaining flight inventory at a significantly higher fare and usually sold at the higher fare. In that scenario, those who purchase speculative tickets early and then cancel are not harming the SWA revenue stream, but actually enhancing it because the seat will now sell (points or dollars) at a higher fare level than originally.