If the city gets some value of having a toxic site cleaned up, then its worth putting some money into that. Whether that is cash up front, or future tax abatements or whatever. The dollar amount of that value is certainly arguable, but there is some value there.
If the developer wants more than that, well then the city should get a piece of the action. You want DSM to put up half the money beyond the brownfield cleanup? Well then DSM ought to get 50% ownership of the entity. That can still be risky, but at least you aren't just giving the money away.
It can still go wrong- iirc Cedar Rapids ended up eating a lot of the ice arena investment when the corporate partner went bankrupt and walked out on the lease. But at least they still owned an asset. I think they broke even, it just took a long time. And they have the RoughRiders which is a popular entertainment option.
What it really boils down to, is there is a not-too-fine line between spending money to benefit the CITY vs just giving the developer a handout so he can make more money. Unfortunately, its way to easy for city government folks to be financially unsavvy, emotionally influenced, or flat out corrupted.