Oh, most of my favorite slash OTPs, I started slashing less because I wanted to see them together and more because I didn't want to see anyone else coming between them. Gen smarm-fic sometimes has similar themes (and Friendshipper's is some of the best! ^^) But slash is often "safer" - you can be sure with slash that a random romantic interest isn't going to be introduced halfway through and take time away from the relationships you care about.