One should not at any time tolerate blasphemy and insults against Lord Visnu or His devotees. A devotee is generally very humble and meek, and he is reluctant to pick a quarrel with anyone. Nor does he envy anyone. However, a pure devotee immediately becomes fiery with anger when he sees that Lord Visnu or His devotee is insulted. This is the duty of a devotee. Although a devotee maintains an attitude of meekness and gentleness, it is a great fault on his part if he remains silent when the Lord or His devotee is blasphemed.
Srila Prabhupada; SB 4.14.32 purport