[pdonis]

> adding it doesn't violate any of the heuristics used to come up with the field equations or action. So to avoid bias, one should keep it around

Yes, that's what I was trying to say. I didn't mean that including it mathematically in the equations necessarily requires one to adopt a non-zero value for it; you are quite correct that one shouldn't do that unless one has observational evidence to back it up (and cosmologists in fact didn't adopt a non-zero value until observational evidence required it).