Let's see, the list of airlines that I can think of that have devalued miles and/or benefits in the past few years, many with little or no notice:
AA
AC
AF
AS
AV
B6
BA
DL
KL
LH
VX
WN
UA
US
Note that this is off the top of my head. I bet I could find SQ/CX/NH devaluations, too...
So as long as you stay out of those loyalty plans, you should be OK. That should be easy to do for someone based in the US, right?
In a competitive environment where all the other airlines are devaluing their miles and, over time, explicitly linking benefits to revenue as best they can, not doing so is leaving money on the table, sad to say.