I'm not against "long term relationships", I suppose in layman's terms I'm probably in one. However, I am however against the sheer level of posturing and bullshit which seems to come as part of the package for most people.
I'm against having your relationship with one person take over your life just because you're fucking them, and I don't see why the people already in your life, your friends and the people who have actually supported you, should suddenly come second to someone you enjoy exchanging bodily fluids with.
I'm also against being "coupley" around other people. That's not a point about PDA, heck I have no problem if you want to fuck each other in the middle of the road, but I hate this weird expectation that you'll function as a single social unit. It's annoying to people who already know you, and outright cruel to people who have their own relationship problems or are single. Basically, I think regardless of what kind of relationship in you're always separate people, if you're so neurotic about each other that you can't function independently you should probably get out of a relationship and get psychotherapy.
I'm also against making promises you can't keep. I don't believe you can promise to love someone forever and ever (unless one of you is dying). The fact is that relationships only work because they mutually provide for people, and the only logical way to handle them is to accept that there may come a time when said relationship no longer provides what someone is looking for. If that sounds harsh, then ask yourself whether any happiness you'd feel from doing otherwise is actually real happiness or just something you've deluded yourself into.
But yeah, there are long-term relationships and long-term relationships. Personally, I think it's very important to build up an emotional connection with the people you have sex with. I just don't think that should supersede or abrogate the equally important emotional connections you've already formed.
I suppose ultimately I don't think having sex with someone makes them particularly special. I don't really see what it changes between anyone, and I'm against treating it as something particularly special and non-substitutable. But I'm very much alone in this regard (heck, even my partner doesn't always feel the same way).