> Most people who (quite reasonably) hate corporate personhood would probably have a knee-jerk reaction that personhood for a river can/should be normalized.
Why do you think this would be the case? I agree with the former but not the latter.
I want personhood for rivers because the rivers near me are being irreparably abused, and anything that can give them greater legal protection is welcome,
Juridical personhood doesn't benefit the entity to whom it is ascribed (directly, at least, and it may not even be a coherent concept for the kinds of things given juridical personhood), it most directly benefits the natural persons given the power to exercise the rights of personhood on its behalf, and sometimes benefits (by means of simplifying their task) the people seeking to use legal process against it.
Well I think one can justify it emotionally or logically. People identifying as anti-corporate are probably more likely to align as pro-environment. The emotional POV would be that non-person-personhood isn't good or bad intrinsically, it just depends if we approve of the area where the doctrine's applied.
The more logical reason is that if corporate personhood sucks and we have it anyway, then like it or not, now we need to extend it elsewhere just to level the playing field. If anti-environmental interests can hide behind it as a justification that makes their fight easier, then let the environmental interests do the same thing.