The question presents on two levels . . . one much simpler than the other. The simpler level first;
As agent of the Owner, you are authorized to make decisions for the Owner for purposes of expediting the project. When the contractor asks you for advice as to what should be done, you, as the agent of the Owner, are speaking as if you are the Owner. The Contractor is entitled to take what you say and rely on it as if the Owner said it. Bear that in mind when you administer contracts.
That is the easy example
The tougher example is your role as you put it "agent of the public". As such, you are vested with the responsibility to make building design decisions that foster the health, safety and welfare of the building using public. While those goals are generally concurrent, as you might imagine, there could be times when they are in conflict.
While it is true that the Architect shoulders a unique form of professional liability that the contractor does not, it isn't accurate to say that the contractor has no liability for faulty construction. In your hypothetical, you suggest that the parties recognize that the ". . . . building design, if built as-drawn, will create an unsafe condition . . . .". That by itself presents a problem. If the building as designed would be unsafe, the Architect has some liability. Given that it was discovered before construction, that liability may be limited to the cost of a re-design that does not suffer that malady, but the fact that the design itself would create an unsafe condition if constructed is a problem for the Architect.
You then suggest that the Contractor, despite that knowledge, decided to construct the work nevertheless. Absent direction to do so from the Owner (or the Architect as agent of the Owner) that really can't happen - i.e.; the contractor can't simply construct the project on his or her own. If on the other hand, the Contractor documents their concerns and the Owner or Architect directs them to proceed in disregard of those concerns, the Contractor may well have insulated himself or herself from any liability - because their only duty is created by the contract to construct the building, and that duty runs to the Owner alone.
In the converse, if the Architect observes the unsafe condition but does nothing to correct it, then the Architect likely has potential liability to the Owner (due to the contract with the Owner - and therefore for the same reasons as the Contractor), but also likely have liability due to the professional nature of the relationship as well. In addition, the Architect would have liability to any third party injured by the unsafe condition due to the obligations imposed by the licensing statute - the "agent of the public" relationship as you describe it.
If the Owner elects to proceed knowing of the potentially unsafe condition, the Architect has a difficult choice to make as duties as agent of the Owner come into conflict with duties as agent of the public. In that example, advising the Owner alone is not sufficient although many Architects believe it is. I have had a number of clients over the years who argue they "got a letter" or some such from the Owner absolving them of any liability for questionable work. That is fine relative to the Owner, but not the public. The Owner can absolve the Architect of liability to the Owner, but the Owner cannot absolve the Architect of liability to the public. In this instance, the Architect must advise the Owner not to proceed. If the Owner refuses to heed that advice, then the Architect must consider disengaging from the project so as not to assist the Owner in the creation of an unsafe condition, but must also seriously consider advising the local building official of the concern. To be sure, an Owner may not appreciate that, but given the duties to the public it is the necessary and proper course.
In reality, refusing to assist the Owner in the creation of an unsafe condition is a benefit to the Owner as well - although they may not see it as such.
Insofar as aesthetics are concerned, due to the extremely subjective nature of those factors, they aren't recognized in the legal sense. While every Architect should strive to create aesthetically pleasing architecture, the question of what would upset a cultural or historical legacy as you suggest is far from settled. While differences of opinion as to what might constitute aesthetically pleasing differ, no one intentionally builds "offensive". Nothing as you describe would therefore get built unless there was a significant view to the effect that it was not in fact offensive.
The law has therefore not ventured into the quagmire that is "aesthetic expression" and because of the inability to extract a neutral principle to apply to those sorts of cases if it did (extraction and application of neutral principles being the hallmark of what the law terms "justice ability") I would predict it never will.
A duty in the abstract to create pleasing design? - yes. Liability in the legal sense for creating an "ugly" or "offensive" design? - no.