Why not invest money in education, training and a social security net that gives poorer individuals the means and space to catapult themselves into wealth?
As for fortress thing - you are exaggerating. There isn't so much crime around these days, much less than 30-40 years ago when things were still going fine according to the article.
In the end, it's just the technology change. 40-50 years ago uneducated masses who were members of solid middle class have been factory workers. They are automated away. There isn't anything which could be done about this. Besides, exactly 40-50 years ago, during Jimmy Carter era, same things were said about farmers who found themselves displaced with great improvements in farming productivity. History just repeats itself.
And yes, classes must be sustainable and moving between them should be difficult, only through exceptional personal (genetic) abilities and a lot of effort. Otherwise they are not classes, just people gambling and some of them winning.
History has shown that once people no longer believe they have a fair chance of achieving prosperity, they revolt. So, even ignoring any other characteristics, your way of social organisation is not stable in the long run.
This is just social darwinism. Not rly a recipe for sucess I can tell ya.