I agree with you that a profit-driven calculus will, at times, conflict with the environmental imperative. However, this is not to say that environmentally business policy will always reduce competitive advantage and a company's profit margins. "Green to Gold" by Dan Etsy is a great book that advocates for environmentally-focused thinking as both a risk mitigator and revenue driver for companies.
I also agreed with your critique of how ineffective flying economy is in reducing your carbon footprint so I omitted it to include train/ground travel as a more effective recommendation.
Your second-last comment is crucial here! I do think you're missing the second part of the question which is "will IBM derive any tangible or intangible benefits from going carbon-neutral?" Reducing one's carbon-footprint comes from a more holistic perspective which moves beyond considerations of short-term costs today to larger questions of brand value, public goodwill and risk mitigation etc. In this vein, it's also interesting to note that a number of IBM's competitors have gone fully or partially carbon-neutral, with probable associated gains in profit and PR goodwill. In 2018, BCG went fully carbon-neutral for all its travel, office electricity use and waste generation (https://www.bcg.com/about/bcg-today/making-a-difference.aspx). An interesting highlight in this article is that many of these measures probably cut BCG's bottom-line costs, such as having offices in LEED-certified buildings, investing in employee bike programs (healthier employees means lower health-care costs). But they are also environmentally-friendly and that is the overlap which IBM should target. To expand on this point, McKinsey also went fully carbon-neutral in 2018 (https://www.mckinsey.com/about-us/environmental-sustainability). These are extremely profit-driven, competitive firms and it would be interesting to learn their business rationale for aggressive corporate sustainability.