Probably because there are reasons for it. People dont wake up in the morning thinking about which airport to hate.
But it's easier to act like theres a bunch of agenda malcontents and that is why IAD has been a historical failure.
The first message you posted in this thread is that Dulles is only used because people are forced to use it. My comment was not saying there are a bunch of agenda malcontents, it was just pointing out there are plenty of people who make ridiculous statements like that.
I have never once said IAD should be the preferred airport of DC, and I am well aware that a majority of people in DC prefer DCA. But the fact remains that IAD serves a purpose and will help handle growth in this region, since DCA is pretty limited in how much it can grow (even if the perimeter rule went away) and it will never be able to handle overseas traffic. If you don't see that, or refuse to accept that, then maybe you're the one with the agenda.
It is not a ridiculous statement. Remove the perimeter rule and see what happens. Premium domestic traffic will shift in the same way that HND is changing routes for NRT. Next, remove the ban on international flights and you likely will see NB intl traffic as well.
DCA cannot replace IAD entirely due to runway and space constraints, but IAD is propped up by restrictions on DCA. Remove them and the market will rebalance heavily in DCA's favor.
IAD could become a more favorable airport for customers, but instead of properly investing in a HSR, there is a slow metro, which will likely follow the path of slow metros to airports in other cities and materially change nothing.
What premium market is currently without service due to the perimeter rule? Just about every major city outside of the zone has service and some have service from more than one airline. So how are you FORCED to go to IAD? United offers service from DCA to all its hubs other than LAX (and IAD), yet those markets are still served from IAD.
If you eliminated the perimeter rule, things would change, but it wouldn't doom IAD because DCA would still be slot restricted. Sure, AA could boost their service to LAX by 10 flights a day and add non-stops to other west coast cities, but that would most likely mean the end of several small to midsize markets that currently have DCA service. AA would have to find those slots somewhere. It's the same story for the other airlines that have a smaller presence. Does DL trim back service to its hubs to add more west coast service? Does it trim back those new BOS flights? In the end, DCA would have more options to major western cities but would serve fewer destinations in the east and midwest. That traffic would have to move to IAD, but not because the airlines were forced to, but because they chose to use their slots differently. The UA hub survived the last wave of perimeter slots that were handed out, and that's when UA couldn't decide what it wanted to do with IAD. Now that it is building it up into a stronger hub, with more connecting traffic, it would have to adjust some things, but it wouldn't disappear.
As for the international traffic thing, you again run into a slot issue, not a rules issue. There are simply not enough slots to replace the traffic at IAD. Let's look at IAD-LHR for today. UA has 3 flights (752/788/777), BA has 2 (777/747), and VS has 1 (333). So how many extra slots would be needed to replace those 5 WB flights, on top of the 1 slot pair to cover the 6th 752 flight? And that's just looking at ONE market. In what alternate reality in your head can DCA cover all of that? I suppose they could find room for an international flight here or there, but like the premium BA flights from LCY have not spelled doom for LHR, DCA's size, runway configuration, and slots will keep it from replacing IAD on the international front.
The problem with your arguments is they are based too much on your personal preferences, and not enough on facts. YOU have no need for IAD, therefore NO ONE has a need for IAD. The facts above show why your original statement was ridiculous. Just accept that there is room for 3 airports in the DC region, that each serves a purpose, and that you don't have to use any one you don't want to.