Not sure what you mean by "justify" in this context, but there is no doubt that Shelley was a revolutionary poet who hoped and worked for a complete change in society. He wanted a society founded on reason, equality and fairness rather than inherited wealth, religious orthodoxy and imposed authority.
The Shelley Resource Page can direct you to many references for this topic; for a quick overview, this articleby Paul Foot is a good place to start.
The Shelley Resource Page can direct you to many references for this topic; for a quick overview, this articleby Paul Foot is a good place to start.