Do interest groups enhance or detract from democracy?

Both, and it depends. How does the interest group operate? What kinds of deals does it make? Whatever the interest, there are good and bad ways of supporting your cause. If a group uses bribery, or makes deals that sacrifice someone else's good for their particular cause, then they detract from democracy by making deals for people's votes and not really representing the will of the people. If they band together to make sure people's voices are heard, then perhaps they enhance it by making sure they are heard... but it doesn't always work that way. On some level, groups that have more money are more likely to be heard... and that doesn't enhance democracy. But if groups are teaching people to be more informed citizens, then that enhances democracy by encouraging more individuals to participate in the process. It is more complicated than just either or.