I happen to be involved in this project in which my advisor has made such a bad decision that the result turned out to be mediocre/uninteresting. While I am not the lead author, I will be one of the co-author for this. In that case, why should I endorse for my advisor's bad decision, when I don't have any means to change the course of this project? I know I won't look as bad as the first author, but still this will be one of my publication. I doubt my advisor will say something like this in the rec: "Oh yes, the bad publication was my idea, my student just followed my direction." How can I prevent this from ruining my future career?
Personally, I can't imagine that being coauthor on an uninteresting paper could "ruin your future career" or even damage it significantly; a paper is a paper, so I think at worst it has a very small positive value. To actually be a negative, the paper would have to be horrifically wrong or plagiarized or something.
Also, not to question your judgment, but you do probably have a lot less experience in the field than your advisor. It's just possible that the project is more interesting to the community than it seems to you; when you're deep in a project, it's often hard to see the context that it fits in to. Consider discussing the project with other researchers in the field (check with your advisor first to make sure you're not giving away too many details too soon), and see what they think.
Even if the project is really worthless, as I said, I don't see it actively damaging your career. Just wrap it up, get it out the door, and start working on something more interesting!
As Nate Eldredge wrote in his final sentence, stop worrying about the past project and start thinking about your next project.
You will be judged much more strongly based on your more recent work so just make sure that your upcoming work is more interesting. You cannot change the past so don't spend time worrying about it. You should spend your time on your future.
One uninteresting publication is not going to sink you unless the science is bad. If it shows you do not know how to do research that might hurt you. If the science is really bad, you might consider removing your name from the paper but since you only complain about the results being uninteresting, let it be and move on to something better.
Judging by your past five questions (in fact, every question that you asked on here), you clearly have issues with your advisor.
I doubt that your advisor is actually that bad. No one can be that bad, and survive academia. It is most likely the product of your not actually caring about your advisor's interests (and vice versa), and the lack of communication between the two of you.
If there is still some time left, I recommend that you seek out another advisor instead of ranting about your advisor on academia.SE, which doesn't actually solve your problems in real-life.
If you are close to graduating, I suggest that you "pay your dues" to your advisor; he let you use his lab and equipment, not to mention granting you access to his expertise, for the past 5+ years. The least you can do is to "suck it up" and pretend to care about your advisor's interests (and put some work into it). After all, you'll need your advisor's letter to stay in academia!