We should not be so idealistic and think that all devotees should be perfect. Unintentionally they can still make some minor mistake. Or as Prabhupada says in the purport to Bhagavad Gita, tenth chapter, verses 4-5 : "Ksama, tolerance and forgiveness should be practised; one should be tolerant and excuse minor offenses of others."
Collected Letters to Friends and disciples Vol 5, Pg 120, 3rd paragraph.