No se puede ver mySQL COUNT desde la tercera tabla

Prueba esto

SELECT i.*, o.organ_name, o.organ_logo, vtable.*
FROM heroku_056eb661631f253.op_ideas i
JOIN
    (SELECT
        COUNT(v.agree) as agree,
        COUNT(v.disagree = 1 or null) as disagree,
        COUNT(v.obstain = 1 or null) as abstain
    FROM op_idea_vote v
    GROUP BY v.idea_id
    ) AS vtable ON vtable.idea_id = i.idea_id
LEFT JOIN op_organs o ON i.post_type = o.organs_id

A la respuesta a continuación le faltaba el grupo por y la condición de unión para vtable