In my field (software engineering), having papers with 6+ authors is uncommon but not unheard-of. Most often I see papers coming out of larger international research projects having many authors, presumably simply because in a large project more hands tend to touch any given piece of research outcome. Further, in larger studies, you sometimes need more manpower to actually carry out the study. If you have a chance to do an interview study with a large group of people, just having one or two interviewers might simply be infeasible because it would take too long.
If you are worried that your large author list will be considered a negative during the review process, this may happen if it is not clear how the large author list is warranted. That is, if you were to publish work coming more less directly out of the PhD thesis of the first author with 7 co-authors, one may ask what the remaining 7 people actually added. In such cases, it is not uncommon to drop subtle hints into the paper about the role of each author. For instance, when you describe your research methodology, you could mention that the first three authors conducted the study, while the remaining three authors were mostly involved with analysis, and the last two authors provided domain feedback and validation of the achieved results (if interdisciplinary).
