“That’s the conventional wisdom. Got any proof that it’s true? Any examples from history?”
Exhibit A: the Libertarian Party. Started in 1971. Has yet to win a governorship, US Senate seat or a seat in Congress. Still keeps on plugging away but has largely been a failure in the electoral realm. That’s not really why they exist, but viewed from strictly that perspective they’ve accomplished little.
Not a Conservative Party, ignores Social Conservatives, as did Barry Goldwater. No party that ignores Social issues will ever change the Socialist parties, either of them.