One of the main disadvantages of proportional representation is that it often does not produce a majority government. It gives disproportionate power to small parties, and the voting process is more complicated. It also reduces the direct link between an elected member and the constituency that the member represents.
The outcome of most elections that operate under a proportional representation system is a coalition government. This is viewed as a disadvantage by many and a disadvantage of the voting system that created it. It is a disadvantage because coalition governments are often less stable than single-party governments elected by a majority.
It is also normal for smaller parties to join coalition governments. This gives those small parties a level of power that is not reflected by the number of votes that they achieved. In many voting systems based on proportional representation, voters do not have the same connection with the people they are electing. There are even some proportional representation systems that work on lists rather than individual candidates, making the connection between the elected politician and the voter even weaker.
Finally, many believe that the actual process of voting is more complicated in a proportional representation system. In a first past the post the voting system, all the voter has to do is select his or her preferred candidate. In a proportional representation system, the voter usually has to do more, such as ranking the candidates in order of preference.