I guess I'm something of a voyeur at heart. When I'm in public I always watch other people out of the corner of my eye, when I'm at somebody's house I always pay attention to the books they have laying around, and when I visit other artists' studios I always sneak a peak at the paints they put on their palettes. Over and over again, I'm dumbfounded at the frequency of use of Alizarin Crimson.
Now granted, this is a lovely color, and a deep transparent red has many important uses. However, its fugitive nature is very well known and documented. Every materials resource details it. Many artists know about it. Manufacturers always label it with their lowest lightfast rating (usually something like "lightfastness=good", or some such euphamism for "you're really going to regret this.").
The urgency and need to use permanent materials is an interesting topic, and one that I'm saving for another day, but this is an extreme case. We are not talking about changes that will happen 200 years down the road. We are talking about degradation and fading of color in normal circumstances that will happen well within the lifetime of the artist (one hopes)... a matter of a few years, even. And it's potentially an ugly degradation, a fade to a weak pink that could skew the color harmony of the entire work.
Obviously, we can exclude from this discussion those hobbiests who paint for the sheer love of it, and don't really care about posterity. Also, to some extent, students can be excused, because student work should be transient. At least, the hope is that with a few year's experience, most artists will do everything they can to hide or destroy their student efforts. By and large, though, I think the majority of us, certainly those who are professionals or have professional aspirations, sincerely want our paintings to be around for a while, and care about using high-grade materials. Even students, when possible, should not get in the habit of using inferior paints and equipment.
Good alternatives exist. Gamblin has a lightfast formulation with the same properties (haven't tried it). I've used Rembrandt's Permanent Madder for several years, and I've just been experimenting with Holbein's Carmine (using a modern synthetic: PR221), and am so far pleased with it. AND YET... every single paint manufacture whose line I've looked at grinds Alizarin Crimson. Each and every one. Well intentioned painting manuals recommend it's inclusion on the palette. Thoughtful artists -- good painters -- continue to use it.
But hey -- it's not the first time well-founded advice goes ignored. After all, every day on the way in I have to scurry past the smokers out for their morning puff...