Gross, but badass.
For the first half of the film, Durden is undeniably badass. He lives above and beyond the rat race that traps the rest of us. He pulls the Narrator out of the prefabricated life he is sleeping through and introduces the fight clubs, which make him feel again. The clubs are a subversive secret that bring color back to the world and reconnect men with their animal side. Durden fights, fucks, and philosophizes like a god. He's like if Neo from The Matrix learned how to fuck, fight, and philosophize. We would all love to become acolytes of Tyler, and that's exactly the point. That's what's supposed to make the second half of the movie such a gut-punch.
For the second half of the movie, Durden is literally a terrorist, an objectively deplorable person with a completely unenviable life. He and his group go around blowing up electronics stores, threatening public figures, and generally doing things that make him look like an exemplary Al-Qaeda affiliate. His coup de grace is blowing up several buildings that hold credit card records in an effort to erase all debt.
20th Century Fox
"It's not terrorism if the Pixies are playing."
Aside from the fact that he's clearly wrong that this would erase all debt, it's also a goal that makes him a complete and utter asshole. Durden outlines his vision for the future by saying, "In the world I see, you are stalking elk through the damp canyon forests around the ruins of Rockefeller Center." He envisions a world set back hundreds of years, which might sound like more fun than working in an office if you're a young, able-bodied dude. If you happen to have been born with any kind of disability, that probably sounds like the indirect murder of millions of people. For all his care to make sure the buildings are empty of any security personnel, Durden's plan would still kill their kid with congenital heart disease. And he'd do it for little more reason than thinking data entry is boring.