It is never better to have a Democrat in any seat or any elected office, PERIOD!
That’s not true. A Rino as an incumbent locks the seat up for many years — particularly Senators. They also (due to the nature of incumbancy) dissuade another Republican from running against them.
Look at Arlen Spectre’s career as an example.
“Arlen Specter (February 12, 1930 – October 14, 2012) was a United States Senator from Pennsylvania. Specter was a Democrat from 1951 to 1965, then a Republican from 1965 until 2009, when he switched back to the Democratic Party. First elected in 1980, he represented his state for 30 years in the Senate. Specter was a moderate who usually stayed in the political center.”
You want more of those or you want to give an honest conservative a shot at the seat?