How can the purpose of capitalism be these two things at once?

[Jeremy]

How can you have a 'tide that raises all boats' and keep inflation down at the same time? If everyone who is making 20k a year suddenly made 30k a year, there would be inflation. If there is low inflation, it means that demand is stable, that no one is becoming capable of purchasing more, which means that class is stable and that there is no social mobility.

Then the question this leads to, how can Capitalism claim to be about what's best for anyone besides the upper classes? Why does anyone believe in something like 'trickle down' theory? Isn't it really 'crumbs from the table to ensure the fortunes of the wealthy?'

And if social mobility is on the decrease and the wealthy are rigging society for themselves, why aren't more people angry? Is it just that America is intellectually decadent and thus incapable of understanding what is happening to them, or do people not mind because of some other reason?
I can't pick any of the current answers as the best answer, I don't think any of them answer my questions and all of them contain at least one idea that I think is outright incorrect. The basis of this question, is why isn't it plainly stated that Capitalism has nothing to do with a 'rising tide'? Larry's accusation of my intellectual decadence, is interesting, but I think it is he that is missing the connection between inflation and class issues. Inflation is then just what the head capitalists call it when growth occurs too fast, when it's at a rate that doesn't threaten to expand demand too much that there are shortages and major price fluxuations. (so no social mobility for you!) And I'm not the one who is confusing trickle down with capitalism, it is the capitalists themselves, the most powerful and successful ones, who foist this obvious bs on the public. I am not about to see neo-cons as non-capitalist, they are it's culmination.
correction, subtracting a doesn't:

"Inflation is then just what the head capitalists call it when growth occurs too fast, when it's at a rate that threatens to expand demand too much that there are shortages and major price fluxuations."

In other words, as long as it's slow growth it's growth, but if it's a fast growth, it's inflation. Meaning that the money supply only can allow a handful of lower class people to move into the true middle class, a handful of middle class people move into the upper class, and like 5 people become millionaires to replace the 10 millionaires who died.

And then social mobility is almost non-existant in america, and social mobility is one of the main reasons this place was built in the first place. You are in a caste, just like in china or india, you will be looked down on by the aristocracy all your life, you will be chided if you try to escape the bounds of your station, your natural place in the order of things, which is out of your control.