There certainly is theory, or at least competing methodologies, behind ETL and Data Warehousing, for a start look at the Inmon vs Kimball methodologies.
In a nutshell (I could talk for days on this subject), Bruce Inmon's (the Father of Data Warehousing) methodology revolved around building a large, loosely 3rd normalized data warehouse from multiple sources, that business domain-centric reporting star-schemas could be quickly built and disposed of as needed, whereas Kimball concentrated on (through some staging steps) building directly into reporting structures.
In my experience, whilst the Inmon philosophy looks the more sensible, Inmon based projects, at least those I've been involved with, tended to fail a lot more than Kimball based ones, primarily due to the time and effort required to build the large Data Warehouse before any business value can be seen.
There is a lot more to it, and I've probably let my own experience and opinions taint the purity behind of the methodologies (you can google for larger discussion), but I mention it largely to illustrate that, even in the simple (hah) process of moving and consolidating data, many a religious war has been fought :) Also be aware that most of my practical DW experiences were about a decade ago, so the field has probably moved on.