When I was younger I struggled somewhat to reconcile doing what a client (or employer) wanted and what I knew was right. Being a stubborn wise-ass, that usually ended up as "my way or the highway" type of a deal, sometimes from my side, sometimes from the bosses. But that has changed over the years into a fine point of ethics combined with professional attitude toward jobs: if something is my job, in other words I'm paid a salary, or per-project, or anything similar where I fulfil a set of tasks or work at goals set externally to me, my duty is to do the things the client has ordered. It doesn't matter if I'm soloing on a project or leading a team, the client has the final word.
Of course, my professional duty is to present to the client what I think is the best course of action and explain why I think so, but that's a "take it or leave it" type of deal. The client is allowed to make what I consider to be sub-optimal choices for their own project, without excessive opposition from me.
I'm sure that I'm not reinventing the wheel here - the same kind of attitude is pretty much the norm among professionals of all trades. There are Reddit forums dedicated to "silly requests" by clients and the common theme is: the client gets what he wants.
I'm not married to my job, and by that I mean that it is emotionally exhausting to feel responsible for choices not made by myself. On the other hand, if I recommend a course of action, and it's accepted, and it proves to be wrong, it's good and healthy that I should feel guilty for making a wrong decision, and do whatever I can to fix whatever fallout has happened from it.
It's a different thing, naturally, for projects I have some stake in, e.g. equity, a percentage of something, or some emotional or physical attachment to the success of the project - for these I'm still the stubborn wise-ass.