Just because you are a member of the program committee you should feel no obligation to actually attend the conference.
If you choose to attend the conference, make sure that every participant is told at the first occasion about your program committee membership. After all, you are a big-shot by now.
Good science is about people and not about content. Thus, it is your prerogative to choose the papers on the authors and their affiliations.
Check if there are any obligations or running feuds and feel free to reject papers accordingly.
You were not selected to be a member of a program committee because you were not opinionated – you were selected for your opinions so express them vehemently. Remember to focus on the person and not the science.
Always remember that function of a committee is to reach consensus rather than the right decision.
If you are on a steering committee, the most important thing you can do is to prevent things from happening – all change is bad by definition. The last thing you want to do is to be constructive. A good strategy is to find philosophical and ideological reasons against the key ideas of the workshop or conference.
A key feature of committees is that there are lots of other people on them – they are there to do the work; you are there to lend your name, reputation and unsolicited opinions.