I disagree with that. You don't have to flip coins with donks in cash games to make money.
If you could know for a fact that you were 51/49 favorite and your opponent would let you get it in that way a thousand times, then sure, that would be a great strategy for long term cash game success.
However, you seldom know with 100% certainty how far ahead you are. So if you THINK you are 60/40 favorite, you might not be. So you are putting money at risk in marginal situations where, theoretically, you can wait for a MUCH better place to put your money in against the same player....like when you are a 10 to one favorite.
If you flip coins in a cash game regularly hoping for a one or two point edge, you are giving bad players a huge advantage. They get to flip with you, and if they win, which they will do half the time, they get your stack. Now when you get a chance to get it in against that same guy when you are a 10 to one favorite, and you double up through him, you end up even for the night against him. Why would you bother to risk your stack the first time, when you could wait to just stack him the second time.
In general, cash game theory says that you should play tighter in cash games than in tourneys. The blinds are not going up and your ability to reload to the max is infinite. That comment you made about being able to reload any time you lose your stack is one reason you play tighter, not looser. You never get blinded out in a cash game. In a 5/10, you pay 15 bucks a round, and, if you just sat down, your stack goes down to $985 after the blinds pass you....you can pull $15 out of your pocket and reload to $1,000 and wait for the best places to put your money in.
Do you happen to have any sources for what you said? I'm always open to read new stuff, but my years of cash game experience and every poker book I have says you should play tighter in cash games and avoid coin flips.