I don't think this is true. Humans are deeply social and copy each other. One can easily see this with young humans, but I didn't fully appreciate this with adult humans before I saw it myself. When I turned semi-custom-vegan, I did hear that it is kind of pointless because animals will still be slaughtered for others. But even suprising to me it turned out that several of the people I interact with started to reduce their meat consumption as well. We aren't all egoistical ignorants that only think of their immediate benefit.

But that example is extreme. There's strength in numbers, even smaller ones. If 5% did what you describe, there'd be that much more people demanding streets that are safe for biking, etc.

If you want to reduce the consumption of some thing, make it more expensive.

Paradoxically: increased efficiency reduces costs and so increases total consumption. This was noted by economist and engineer William Stanley Jevons, in the 19th century.

There are different ways of increasing costs, and not all necessarily involve prices (or taxes), though those tend to be the most effective and easiest ways to do so. Legal, social, and moral costs can also be imposed (criminalising use, making use anathema, making use taboo), but these take time to impose and have various side effects.

This is a difficult problem, and even recognising the dynamic is difficult. It's deviled ecolologists, economists, politicians, and others, for over two hundred years (and arguably, for over two thousand).

Seriously, you want to make real impact, learn yourself a high energy physics degree and do research. Not eating meat is a joke. We as humanity will make not eating meat much sooner if we'd focus on uploading and fusion.