I find the tone of your comment quite harsh in its choice of words. Just as you call the author a "doctrinaire doomer" for not showing huge optimism about the future of our way of life and civilization, you could be labeled an "infantile dreamer" and "deluded denialist" of the very real and concerning findings about the climate change and planetary limits we will be faced with, and already are.
But is such pointed labeling really justified? And more importantly, what good does that kind of barbed language do in a conversation.
The blog post author seems to be concerned about the time and attention spent on something that is not likely (i.e. as his post states is off by several orders of magnitude at least) to realistically help with alleviating the urgent problems of planetary climate change and resource exhaustion. I agree with that concern.
Faced with finite resources and a time limit, prioritization is essential to ensure the best chance of success. Technologies like fusion detract from finding and implementing more realistic approaches that could help with long-term civilizational sustainability.