The argument doesn’t discuss all the factors that lead to environmental progress, and definitely doesn’t say that fear created by radical environmentalists is the most important factor.

This is a good paraphrase of the conclusion. The editorialist’s argument is designed to suggest that the extremists, by spreading fear, can motivate environmentally-friendly change.

This is much broader than anything the editorialist claims. The argument is specifically talking about inertia on environmental issues, and not inertia in general. Also, the argument’s actual claim about inertia is a premise, not the main conclusion.

The editorialist doesn’t tell us anything about the motivations or intentions of the radical environmentalists, so we simply don’t know if this is true.

The editorialist never claims that radical environmentalists totally ignore facts and practicality, even if they sometimes make false claims or make unfeasible proposals. This goes beyond what the argument actually says.