Among all the current legislators whose religion is Roman Catholic, what is the percentage of the ones without an instagram account?
religion is Roman Catholic refers to religion_bio = 'Roman Catholic'; calculation = MULTIPLY(DIVIDE(COUNT(instagram is null), COUNT(bioguide_id)), 1.0)
SELECT CAST(SUM(CASE WHEN T1.instagram IS NULL THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM `social-media` AS T1 INNER JOIN current AS T2 ON T1.bioguide = T2.bioguide_id WHERE T2.religion_bio = 'Roman Catholic'