Surah 2. Al-Baqara, Ayah 12

It would seem that this is an allusion to people who oppose any "intrusion" of religious considerations into the realm of practical affairs, and thus - often unwittingly, thinking that they are "but improving things" - contribute to the moral and social confusion referred to in the subsequent verse.

Much mischief is caused (sometimes unwittingly) by people who think that they have a mission of peace, when they have not even a true perception of right and wrong. By their blind arrogance they depress the good and encourage the evil.