pro - governmental representatives are typically voted into authority by groups of people (except US supreme court justices)...
pro - democratic governments have local and centralized governments which means the work load gets spread out, and different forms of congress or parliaments create a system of checks and balances.
pro - due to the fact that most everything involves so many people democratic governments are more resistant to corruption.
pro - most democratic governments help support each other and currently embody ideas such as freedom of the press, freedom of religion, freedom of speech, and equal rights.
pro - in most democratic governments you work for yourself. you get to vote on how much taxes you pay. Thus most of your earnings go into your pocket. Thus democratic governments tend to have a higher standard of living. (this gets complex)
pro - democratic governments are less likely to go to war, due to the fact that more people have to decide that war is a necessary and beneficial to the public vs. a single leader, or commity deciding to go to war for the benefit of a few individuals (at least that's the theory)
pro - most democratic governments are not run by religion, which means law is decided to be fair by congress and voting, vs. getting morality out of a book, without having a say.
con - due to the large amount of people involved in making decisions. Federal regulation, law, and infrastructure takes forever to implement. vs. a dictatorship where leader just says "do this..." and it gets done.
con - because representation is supposed to be about the majority vote... it means minority groups can easily get the shaft.
con - the governmental structure of democracy has never been able to work purely by itself... most democratic governments are democratic republics or democratic parliaments. What this means is that for a true democracy everyone has to know everything about politics to make an educated vote... that's what democracy means, everyone gets to vote. However since that doesn't work, we vote in representatives, who are supposed to vote for large groups of people. That means your representative can't always represent your values, ideas, etc. in government.
con - most democratic governments by nature will always have national security issues, due to the free movement of people and objects within the countries borders.
con - most democratic representatives pander to different ideologies or lobbist groups... which means that grid lock, and party politics keeps politicians from actually making representative decisions for the public