This is the context from Joel Spolsky's blog:
And now I'm going to get a little bit mushy, and argue that the most
productive programming environments are the ones that let you work at
different levels of abstraction.
The meaning of mushy as in Cambridge dictionary doesn't quite fit in here. What does mushy mean?
Best Answer
This is a term used to indicate that, while the preceeding arguments were as objective and well-supported as he could make them ("hard" or "firm"), what follows is more subjective.