Expression v. Technique

The eternal question: what is the conductor's responsibility to the ensemble, a technical clinic of all conducting gestures to completely execute the composers music to the letter, or an emotional filter through which the ensembles music is expressed? With new friends beginning their conducting sequence at UAB, this old question popped up into my head. I have been under conductors and watched conductors who ascribe to both philosophies, I want to know some other people's opinions. This also leads to another question, and one I would like to get some opinions on as well. What does the conductor owe to the composer in a performance? What should be observed and kept in the performance from the composer? Hopefully, these composers are musicians and will use appropriate instructions, but what are the boundaries to be set for the conductor? and what are the ramifications if the conductor disagrees with the instructions of the composer, but likes the piece enough to perform it in his/her own interpretation?