The goal of the Kyoto protocol is combating global warming. It faces many criticisms and is even claimed to be a failure. However, few different reasons can be cited for why people want it.
The members, who prepared the Kyoto protocol, wanted it to legally mandate the countries that ratify the protocol to take all the proper measures to reduce the greenhouse gas emissions and save the environment.
Environmentalists want it because they feel that it is a safe way to save the planet. They opine that right now Kyoto protocol has attainable targets and any future negotiation will only bring in stringent targets.
Many feel that the Kyoto protocol is a good first step and method to combat global warming and will be a good model for future global treaties.
Some see it as the only existing option to solve the global warming problem, so they want it.