As in so many cases, all this can depend on the individual's particular situation. In my case, when I converted in 2008 the taxes were paid from the taxable money account. I was going to have to pay those taxes eventually anyway. So I saw this as a chance to move part of a 60/40 portfolio to a tax free on withdrawal Roth at a time of lowish valuations. It was a scary and unpleasant time and this was one tactic that I felt was a positive one
given our resources. Now if we were on the edge of portfolio survival that might be a different story.
Now suppose the market just kept going down as in the 1930's. Then it would be a lot tougher on me. Maybe I just got lucky!
Here is a chart comparing the 1929, 1987, and 2008 declines. The red arrow shows where I made the Roth conversion. I think Cut Throat was right in 1929. I just got it right in 2008 -- luck or skill? That is life I'm afraid, scary.