Why is 尊重 considered 不礼貌 in this context?
First you have to know the difference between 尊敬 (respect) and 尊重(respect)
尊敬 is respect with admiration. For example, &quot;I respect my teacher&quot;; &quot;I respect scientists&quot;
尊重 is respect with acceptance or tolerance, mostly treat as equal. For example, &quot;the court respect the defendant's right to remain silent&quot; ; I respect your opinion (although I think it is stupid); I respect women's right (although I think men are superior)

I would not go as far as saying it is impolite to use 尊重 when you should use 尊敬; it is just not respectful enough

Beside 尊重 is not 尊敬, the problem with the sentence &quot;我尊重中国的工程公司&quot; is that we don't know in what aspect you respect Chinese engineering companies. Is it their reputation? If it is their reputation, then what kind of reputation you are referring to?
The topic: 'Chinese engineering companies' is just too general to pinpoint what is the respectable element, we need something specific, for example, &quot;I respect Chinese engineering companies' innovative thinking&quot;

&quot;在我们国家中工会受到人们的尊重&quot; implies people respect the union; not unlike the way you respect your neighbors
&quot;在我们国家中工会受到人们的尊敬&quot; implies people respect and admire the union. We all know the union's reputation is protecting labor's right against big companies' unfair treatment of their workers

Note:
尊敬/ 敬佩 = respect and admire; 敬重= respect and value; 佩服 = admire; 尊重 = respect (as equal)