Sure James Harden in Brooklyn could turn out to be a disaster, but the Nets absolutely have to attempt to land him. If a player of that caliber wants you, you don't say no. It's basically that simple.
Franchises do whatever they can to net a player like him. Some never have. I understand there are plenty of people who don't love his playing style, however, there is no questioning his value. Harden has been top-three in MVP voting in five of the last six years. And the Houston Rockets are the only team in the NBA not to miss the playoffs since he was traded there.