That says the opposite, actually. He's saying that lack of full immunity would make presidents think twice about fighting the peaceful transfer of power
You should re-read it:
As he considers immunity in a case centered on a president's refusal to accept his electoral defeat, Justice Samuel Alito suggested that
not giving presidents immunity will actually discourage peaceful transfers of power.
Alito pressed Michael Dreeben, the attorney for the special counsel, on the idea that
an outgoing president who looses [sic] a hotly-contested election will be disincentivized from leaving office peacefully
because he will fear prosecution by the administration of his successor, a "bitter political opponent."