First, this would have been a better comment without the anti-Catholic bias. (Yes, that's what I saw here.)
Moreover, while it's certainly true that one individual's choices have infinitesimal impact globally, it's also true that if every individual makes the same calculation...nothing changes. The tragedy of the commons, again.
But to be frank here... people decide that relatively minimal sacrifices are simply too much to bear, and they rationalize that, because "I'm just one person, and it won't make any difference." Multiply by 8 billion.
It's a human nature problem. Humans live, experience, and largely think, in the short run. We don't deal with long-term challenges particularly well; we rationalize and kick cans down the road, until we just can't any more. Some of us try to see the longer-term, and respond accordingly; but that's an act of the intellect, and it's in tension with more basic drivers of human nature. Societies have collapsed because they couldn't cope with long-term problems caused by short-term decision-making. We're technologically more sophisticated, but still basically the same creatures.
When we're confronted with a problem that has to be addressed 50 years before it becomes critical, or else it's simply too late... we're not likely to be able to address that problem, as a society. Individuals - some individuals - can, but society as a whole. Not likely. But that doesn't mean that those of us who see the problem shouldn't advocate for changed behavior, even if we (mostly?) expect that advocacy to be largely ignored.
I'm not an optimist. In general.