D is wrong because of multiple reasons. First, it unnecessarily uses future tense. Second, "to propose, pass, as well as to repeal laws" isn't parallel.

Hope that helps..

D is wrong, because it should be "to propose, to pass, as well as to repeal laws"

Parallelism of the infinitive needs to be conserved throughout a list.

There is growing demand in the state for “initiative and referendum,� a procedure that allows voters to propose and pass laws, as well as to repeal them.

(A) allows voters to propose and pass laws, as well as to repeal them --> Cream of the crap...best choice!!
(B) allows voters to propose, pass, and to repeal laws --> to propose || pass || to repeal laws ( parallelism issue )
(C) allows voters to propose, to pass, and repeal laws -->to propose || to pass || repeal laws ( parallelism issue )
(D) will allow the voter to propose, pass, as well as to repeal laws -------> This is out because a procedure is singular..so needs allows
(E) will allow laws to be proposed, passed, as well as repealed by voters -------> This is out because a procedure is singular..so needs allows

D is wrong because a single voter can not pass the law.