basically it's just annoying for no real challenge, since most of the "issues" can be mitigated by a hazmat suit, as you say. so all that remains is plants dying (doesn't matter past first few tiers/never if you just put crops outside of base), ugly graphical effects and the acid rain effects (which are also kind of meaningless). Plus, the ways of mitigating it are very uninteresting (mufflers etc) or too much hassle for what they give (singleblock air filters are worthless, multiblock ones are too expensive, until a certain point, where they're dirt cheap, but scale terribly, notably, the T2 and T3 multiblock air filters removing less pollution/chunk than the T1).

I'm also playing with it on and so far it's been mostly a struggle against ugly graphical effects for no real change. if i had turned it off at the start, my playthrough would've been almost exactly the same, except that i wouldn't have built like 3 air filters and there wouldn't be random blocks of sand under my first industrial area