Communism gets a bad rep because of the people who have used and abused it. The theory of Communism isn't inherently bad or evil like some uninformed people might choose to believe. At its very basic definition, communism is just a way to ensure that everyone is treated equally and fairly and that everyone is given what they need by the state.
Communism strives for a perfect, utopian society in which there's no racism, sexism, classism, no one goes hungry, everyone has a place to live, etc. The world as it stands isn't perfect and is far from a utopia and Communism is an attempt to fix that. Communism would require lifting up the poor and bringing down the wealthy through a redistribution of wealth so that everyone is on the same level. It was born out of an attempt to free the working class from the whims of the upper class, to eliminate competition so that everyone can benefit instead of just compete.
The hang up comes in because, in order to start the process, the state has to control and distribute goods. Communism, played out correctly in full, would result in a stateless society, where everyone helps everyone because all goods are owned and shared equally by all of society, so that society is classless, moneyless, and ultimately stateless, with no oppression.
The IDEA of Communism is a good one. Unfortunately, it's practically impossible to put into place, because Communism requires all of society being on board and then it requires the entire WORLD to be on board as well. Capitalistic countries rail against this idea and then you have the whole anti-Communism stance that ended up causing things like the Red Scare and the Cold War. It doesn't help that tyrants took hold of the theory and warped it to fit their own needs.
The pros are the theory itself - it's just an attempt to create a perfect society where no one suffers and everyone is treated equally and there's no oppression.
The cons are that we're all human and it's a lot of power to give to someone... who will ultimately abuse it and twist it into something it was never intended to be.