Is citing only high-impact articles in my publication ethical?
No, omitting work you know to be relevant simply because its publication venue does not have as high an impact factor is not ethical.

The purpose of citations is to point your reader to the relevant additional literature, give credit to the work that came before you, and position your work in the broader space.  Indexing the most prominent venues (and thereby reinforcing their prominence) is not one of their purposes.

If you read the paper, and it materially impacted your work, you should cite it. And you should cite other papers that are relevant.  You don't have to cite every thing that has ever been written on the topic (and as Googlebot mentioned, review articles are a great thing to cite), but quality of individual papers, not prestige of their publication venue, should be the deciding criteria.


  This is refutable by saying "Interesting work always gets cited and gets popular, irrelevant of the journals impact factor."


I do not believe that refutation, but even if it were true, it would not be true if authors approached citation as you are proposing.