I-11 is not needed South of I-8.
Agree. Most of the route is parallel to I-10.
Indeed, you could just widen I-19 between Nogales and Tucson, and I-10 between Tucson and Casa Grande, with maybe a western bypass added around Tucson. Then widen I-8 from Casa Grande to AZ 85. Let that junction be the southern end of I-11, then simply run I-11 along the AZ-85 right-of-way to I-10, then onward up to Wickenburg, where it can then follow US 93 to the Pat Tillman bridge south of Hoover Dam.
That would be one way to avoid the environmental impacts that concern people.