In the end, the most important thing is making the shot. If you make some blanket rule of, "I never use the pop-up flash!" then I question you as a photographer.
A bad shot due to equipment limitations is better than no shot at all.
If a speedlight is not an option, then I can agree with you if we're talking about a snapshot/family event/once-in-a-lifetime type of shot, etc.
So in other words, we're in agreement. There is a time and a place where the pop-up flash could be used. I hate the thing too, but if that's the only way I can get a shot, I will use it, and apparently you will to. I'm going to Disneyland next weekend for my daughters birthday. Since I'm already going to have to carry a backpack full of stuff for us, I'm in a situation where I need to limit what I bring in. I will likely bring only my camera body and a lens. My strobe just takes up too much precious space. If I need to make a shot, I'll use the pop-up because I need the shot. It would be stupid of me to miss a shot, simply because the lighting is too harsh and flat. People like to make these absolute, blanket statements about photography (I always, or, I never) when all that's doing is limiting themselves.
If I am doing a model shoot, and I forget to bring my lights, am I going to use the pop-up flash? No way. I'll likely get fired for being an unprofessional, unprepared photographer. But if I'm out shooting for my own sake, and I don't have a particular piece of equipment to make a great shot, I'll make do with what I have. It is foolish to say that you'd rather not make a shot than have to use the pop-up. You could miss the photo of a lifetime.
This goes along the lines of the people who will say to "never go above ISO 800 because of noise!" or "you always need to follow the RoT!" You simply cannot make absolute, blanket rules when it comes to photography. We, as photographers need to be able to adapt and use whatever equipment and skills we have on hand to make the shot, and not resort to ignorant, absolute statements that end up stifling our creativity.
I don't use my pop-up all the time, and actually, I rarely use the thing, but I'm also not afraid to use it if it's the only way to get a shot. As was in someone's signature, who actually made the statement they would rather not take the shot than to use the pop-up, "You miss 100 percent of the shots you never take."
EDIT: I just want to make it abundantly clear, I don't really agree with the OPs premise. If I saw a bunch of people at a party using DSLR's without the pop-up flash, I would likely shed a tear of happiness to know that they are doing what they can to make their photos look nicer. I don't like the pop-up flash, and I will shoot at max ISO and down to a shutter speed as low as 1/15 sec before popping up that flash. My point is that if you need to use it, use it. Don't make absolute statements that end up killing off your creativity. A missed shot can never be re-taken.