You are welcome to your opinion, and to your own moral code.
Mine means I do have that obligation.
I suspect many share this aspect of my code, which boils down to "keep your commitments, both explicit and implicit."
Nobody hires a full-time employee expecting that they'll start slacking off once they get the basics of their job going smoothly, and I know that going in (as do most people).
Thus, if I plan to do that, I have to warn them up front that our expectations are likely not aligned.
If I don't want to have that obligation, then I can negotiate up front, or take on the risk of being a consultant or startup founder.
Thought experiment: ask yourself whether you'd hire someone advertising my work ethic or yours, if all other aspects are equal between the candidates.
Then ask yourself why you answered as you did, and which response the market will reward better in hiring.
My reason for this stance is my personal code of ethics, not pragmatism, but I think the pragmatic consideration may clarify my point.