How much is submission acceptance to high-profile conferences influenced by internal politics?
It is an often-heard prejudice in CS that many of the top conferences are relatively closed "boys clubs". Indeed, if one just looks over accepted papers for multiple years, one typically ends up seeing the same affiliations over and over again, strengthening this impression.

However, this could be due to a number of (good or bad) reasons:


Papers from professors / labs that are well-known in the field may simply be of much higher technical quality, making it quite natural that they also get accepted much more often.
Professors / labs that are well-known in the field generally know how to write papers for this specific conference. They know what the TPC values, and how to present their results in a way that is appreciated in the field. As these professors are typically in the TPC themselves, they know what kind of papers usually get accepted and which are rejected.
Professors / labs that are well-known in the field often have a better grasp on the existing state of the art in the field, making it easier for them to identify what is good and novel. In my experience, "outsiders" have a tendency to overestimate the novelty of their contributions significantly. Further, well-known labs know what problems are currently en vogue in the community.
It is of course also perceivable that papers from well-known professors / labs are just not judged as critically. For instance, a reader may very well think that a paper is not applying a given technique correctly, but as the paper comes from the group that invented this technique, he gives them the benefit of doubt and assumes that they will know the technique better than him. He would probably not extend the same favorable thinking to an outsider.
Finally, for some topics, it is just easier for some labs to do good research than others. A common example are the web search tracks at the WWW conference. These tracks typically require the validation of new algorithms on real data, to which mostly only industry labs from Yahoo! etc. and their close collaborators have access.


Note that none of these reasons is really politics. Indeed, I would argue that all of the reasons above are significantly more likely than a paper getting rejected for the reasons you cited.


  I assume in good faith that most of the editors may not reject papers without reading them


I would say, at a top conference such as CHI, you can rely on your paper at least getting reviewed thoroughly, yes.


  but does anybody concur with opinion of professors at my department?


Well, given all the reasons above, it is indeed quite likely that your paper will be rejected. By definition, if a conference has a &lt;20% acceptance rate, rejection is always a real possibility (clearly, it happens to most submissions). However, I am wondering why it would be better to not even try if you think your work is good enough for CHI. If the paper gets rejected there, you can still re-submit to a lower-tier venue, and you receive a number of hopefully helpful reviews. The only disadvantage I see is that it prolongs the publication process by half a year, but if you see any chance of the paper begin accepted at the top-tier venue, I think this should be worth it.