[If Democrats are worried about the effects of the replacement plan, they should be proposing their own ideas, not just placing blame.]
Because Republicans are certain to listen to any idea they propose? Oh wait, its the other way around in today's hyperpolarized partisanship in Congress.  That was actually my biggest gripe about the Obama administration.  He kept trying to go for the win-win when Republicans in Congress made it clear from day one they planned to do everything going for the win-lose.  I still remember how the three credit bureaus warned of negative treatment if the budget only included spending cuts back in 2010.  Obama kept trying to negotiate some revenue increases but the Republicans held out for only spending cuts and got what they wanted which resulted in negative treatment of US credit rating.