That's why I don't like seeing 100% goals. Everyone knows it isn't going to be accomplished, so why not have real, specific policy planks instead? So everyone knows what to expect, and can work with the upcoming problems, instead of being held responsable[sic] for failure to meet an unattainable goal.
Because to every company in America, "working with upcoming problems" means "weaseling out of our obligations to everyone but our shareholders." If you propose a carbon tax, that means paying lobbyists to shoehorn in an exception for their specific industry or getting the state to give them a tax break to offset it or any of the other games companies play with money -- or just flat-out ignoring it and daring someone to sue about it. If you propose a <100% reduction in nonrenewable power generation, that means establishing that their particular concern should be in the nonrenewable fraction for whatever reason, or that the percentage should be dragged down to meet their needs. Historically, what is "achievable" has been twisted by conservatives to mean what doesn't need them to change anything, so the less wiggle room one starts with, the better.
Then, too, specific policy planks aren't compatible with American policy. Debating about things we don't understand is almost a sport, here, as is demanding to be taken seriously for no good reason. If you give people a target number like 95%, you will get a hundred million armchair experts on Facebook parroting the same factoids about why it should be 90% or 99% or 0% or my ideological opponents should die in a fire%; if you give them actual policy proposals, they will find or invent some consequence they disagree with or mine a quote they think sounds dumb and bikeshed about it just for the sake of sounding impressive until the news cycle turns over.
Don't think of the 100% proposal as a law; America doesn't do those anymore. Think of it as a slogan to rally the mob behind our next dictator, something short and memeable to chant in the civil war to come. It serves well enough as that.