As Jason mentioned, the points you made here are far from universal, so claiming that "refinancing your mortgage is costly and silly" is misleading at best, and flat out wrong at worst.
Addressing your first point, there's no question that there will be closing costs involved, but all that means is that your expected savings need to be significantly greater than that extra cost. For example, if your refi closing costs are (say ) $2000 and your new interest payments are lower by $200/month, you'll more than make up the difference if you keep the new loan for a year. This does neglect the fact that you'll have more payments to make on the back end of the loan, but you can easily figure that out too by comparing the expected total interest payments over the life of the current vs. new loan.
To your second point, moving to a longer-term loan may not be pointless. Depending on the details of the new vs. old loan, you may end up better off refinancing once you consider the impacts of inflation and tax benefits. You can see more details of that here: https://medium.com/financial-strategy/why-prepaying-your-mortgage-is-almost-always-a-terrible-idea-88fa87977d77.
To your third point, I mostly agree, and have never taken an ARM. However, if you know for sure that you'll move out of the home in say 5-7 years, then getting a 5-year or 7-year ARM is the financially savvier move.
To your fourth point, investing in the market does indeed come with risk. However, over the long term, the market is one of the best wealth-building opportunities available to most people. Over the past century (including the Great Depression and the Great Recession), the market returned an average of about 10%/year. Thus, if you consider a 20- to 30-year term, the market will almost surely provide a better return than prepaying your mortgage principal. Similarly for the refi.
Your fifth point is golden. Doing a cash-out refi in order to finance consumption is (almost always) foolish.
I'm not completely clear on your sixth point, but it sounds like you're saying that a refi is best (and probably taking as much cash out as you can) if you expect to lose your income, and presumably default on the loan. The logic might be that you'll lose your home anyway, so may as well get as much cash out of the deal as you can. If that's what you meant, then I agree with the math but question the ethics.
