To "alarmists" both "climate change does matter" and "China isn't the only problem" are valid arguments because that's a logical AND: "it's a problem and we're causing it, so we should do something". When you inverse it you use DeMorgan's law and you have to disprove one, either "it's not a problem" or "we can't do anything to stop it" but they typically do it in a way where one purported disproof invalidates the other, for some reason. They argue both "it's not a problem" and "it's a problem but we can't do anything to stop it".

To alarmists both arguments are valid - just use whichever one is more convincing to the person you're talking to. The objective is stop using fossil fuels no matter what.

Im not sure what is this type of debate good for.