The pluralist theory of government is rooted in the idea that not one special interest group wins all the time. The idea here is that some groups win and some groups lose, and as long as that balance is maintained, special interest groups increase citizen representation. The problem here is that some groups do win all the time. Groups that have greater economic power end up exerting greater influence. These groups win all, or most, of the time and cannot be defeated. Powerful special interest groups that are able to lobby effectively end up having their interests represented more than others.
It is to this point where I think that the pluralist line of thought lacks some degree of real world practicality. The theoretical idea behind interest groups should ensure all citizens' voices are represented. Yet, the practical application of this theory tends to display that groups which are more powerful in terms of economic reality and are able to use the lobbying system more to their advantage tend to have greater influence over policy direction. In this reality, all voices of citizens are not entirely heard.