Your negation is way too strong, an ever-growing number of people do, in fact, take their personal footprint into account for every decision, my family and myself included.

I don't know about your anecdotal joke about some German activists flying 20k miles in half a year, but it's also a fact that flygskam is growing, that people who can afford it reportedly take a train even when it's slower, and that airlines are looking into carbon offsets. Another anecdote, my local XR group has a car pooling mailing list to make sure they attend all demonstrations in a convenient, low-carbon manner.

The math is simple, every liter of fuel kept in the ground will slow down global warming. There is no "threshold" that we will reach at which point all humanity is doomed.