I imagine most members of Hacker News feel like they probably do pretty well financially.
Even if you think that way, your quality of life could potentially take a massive leap if you are able to retain your current salary and move to a lower cost area.
Don't waste a once in a lifetime opportunity for you and your family.
Arguing that a massive increase in supply should not result in a price drop because of some fairness idea is like arguing that a ball should not drop to the ground because of some ethical concern (e.g. it may drop on someone's head). Look, that ball is gonna drop whether you like it or not, there is no amount of tweets and open letters and hunger strikes that will prevent that ball from dropping.
The only way to prevent the ball from dropping would be to try to make working from home illegal, thus forcing Morgan Stanley to hire from a much smaller labor pool.
Now there is a flipside to this, because the above argument was just for the highest paying employers. Lower paying employers will need to pay more, because their workers can now be poached by Morgan Stanley. E.g. Expanding the market increases supply for the highest paying firms but decreases supply by the same amount for the lowest paying firms. They are going to feel a big labor crunch, particularly those firms that opened up shops away from SF/NYC in order to pay low wages.
But the end game -- e.g. competing with global labor -- is going to be a big threat to Silicon Valley wages, especially for individual contributors.