I do not know how to answer that. You need technology in place for both. You need order flow for both.
No, the less order flow, the more challenging. Making money as a MM in any asset class requires transactions. If your strategy and risk management is sound, the more trades you do the more money you make. That simple.
The majority of the times a stock is not crashing or spiking. So this is not a valid argument. Also there is no guarantee that they will make money. There are no hand-outs and everyone assumes some risk. Third keep in mind, that regardless the direction or volatility in the market, there are buyers or sellers. Even as a security tanks, if there is volume on the security, then there are people buying.
Flash crashes have shown us just how few limit orders there are without market makers outside a narrow band.
Yeah but they all stop crashing and start recovering sometimes immediately in the same session. Ever wonder why?
Most of the market making occurs within a single asset and is based on the state of the various order books across multiple exchanges. Conceptually, it is fairly simple - you show bids and offers, trying to retain priority as much as you can and hoping to have trades bounce between bid and ask. Your worst fear is negative selection so you end up doing two things - skewing your markets based on various alpha signals and having an adversity model that would cause you to pull these orders. That could be either based on the information specific to this particular stock or based on the broad market. For example, as an MM you probably have an MW feed from up north and can react quickly to moves in ES, but it's not likely you trade the ES unless really forced to.