I think that's the only reason you need, just like you can't have a reason to justify doing what you believe is wrong. Of course these are goals I would aim for, I simply mean that if I fail to live up to these standards then I am failing,not that I claim to have succeeded.
There is always an authority,even if that is yourself. If you consider yourself as the final authority over all things then I suggest checking your ego a bit.
My perspective: As in any program or system of programs,the author has original and final authority over all things authored. Even if you leave absolute origin as a variable,it is clear that both natural and man made systems which have legitimate authorities.
But in the case of your question, I say ask and answer deeper questions. Who or What has authority over interpersonal interactions at the social , relationship,national,global and universal level. An authority that depends on your opinion of it's legitimacy is not legitimate.
To answer your question directly- it is harder than it looks
To your original point, no, there would be no point to being honest if being dishonest made it easier to get ahead. But it would be very naive to presume that being dishonest makes it easier to get ahead. You need to have cunning to get ahead by being dishonest, and one false move can screw up a long period of well executed dishonesty. Are you personally equipped to pull that off? Better than those who've been practicing their whole lives? And beyond that, the psychological and sociological ramifications of it will catch up with you too. Who do you think you'll tend to be surrounded by if you take such a strategy? What kind of life experiences will you never get to experience as a result of that? You don't have to look very far to get answers to that. It's not pretty.
For some people, pure wealth or fame is worth any degree of dishonesty, by which I mean the negative effects of it simply do not cause them difficulty. But I think the far more likely case is that our societal discourse minimizes the difficulty it does cause. When peace decays and order crumbles, it doesn't make warfare (literal or figurative) any less expensive or unpleasant. It just makes it harder to avoid.