Not exactly sure how you figure that is the fault of former Democrats who switched to Republican, however. Seems to me, the problem with the GOP "leadership" (you scare-quoted the wrong word) is that they've gone Washington - and they were perfectly capable of doing that while having always been registered GOPers. The answer is increased conservative vigilance, challenging RINOs in the primaries, and term limits - not driving away potential allies and elected officials because they used to be Democrats.
I think dems go to where the power is regardless of power. The problem with allowing a switch is now you have a democrat in a republican office getting election funding from republicans.
A conservative wanting to run for the office will get no funding from the republican party. These switches force conservatives out of the election process unless they self fund.