I don’t recommend making significant changes to activity levels at the same time as making diet changes. Weight loss comes from changing what you eat. Exercise is absolutely necessary for a healthy lifestyle, but it is not the major factor in weight loss. And increasing exercise behaviors can destabilize eating habits, making it harder to stick to any good changes you do make with either diet or exercise.
The core is about change. To accept climate change means they have to make changes to their lifestyle, and they don’t like having to change. Beyond that, it’s rationalizations and bad faith arguments from the usual grifters and corporations layered on top of that to justify the position they chose emotionally.