Having observed the discussion over on the "Unpublished let downs" thread, it is taken as read that to remain at or above MSA in IMC is "safe" yet to even consider a descent below it is "unsafe" unless on a published let down procedure (of whatever sort), precision or non-precision.
It's generally thought to be a good idea to have a red line,
decided in advance, which you
don't pass "just a little bit, just this once".
We'll all have some of our own personal red lines, re crosswind, spare fuel[#], whatever. Others are laid down for us, such as the 90 day rule and MSA. I'm quite happy with this, it saves me having to work out my own, which in the case of MSA would be on the basis of not enough experience.
[#] Yes, I once called the fuel truck because the aircraft had 1 gallon less in it than I'd calculated, including generous reserves.