That only moves the question up a level: why is it wrong to do X as your goal, but okay to do X in service of something else, even if that something else is as vague as aesthetic reasons or whatever impels people to randomly design things? By your initial reasoning, it would be wrong to design spikes to discourage the homeless, but okay to design spikes if you just happen to like the look of spikes, even though both of these have the same effect.
why is it wrong to do X as your goal, but okay to do X in service of something else
Because intentions matter for judge morality of a lot of human interactions. If a professional is hired for a specific purpose, it's important that the professional doesn't use the power of his role to push his personal agenda.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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