If automation implicitly increases wealth, why is it generally considered undesirable?
Short-term or long-term, Property rights and distributional issues exist, "evil capitalists" or not, and they will always result in strong scrutiny of any change.  Remember that what is "short term" for society is mid- or even long-term for individuals.

Moreover, there exists the transitional pain: whether we can optimize it downwards, and who is going to feel it.

All these cause the heated arguments and the opposing positions.

But your post starts with a strange assertion: that "almost all times" it is assumed that automation has a negative economic impact. If this was so, it seems a little strange that automation marches triumphantly for the last two hundred years, and it continues to do so. If this was so, people now must live in a much worse material situation than two hundred years ago. Is this the case?