How to combine between not warning against the opposers (to the Qur'an and Sunnah) and clarifying the straight path?

First of all, you teach them the right path and they will know the opposers (to the Qur’an and Sunnah). However, if you forbid them while they don’t (even) have principles or knowledge, this is of no benefit, rather it only begets enmity. Teach them the right path and the religion of Allah, then after that, either they will know the opposer or you warn them against him, if they don’t know. But if you begin with them by insulting so-and-so and defaming so-and-so and not… this is not correct, while he doesn’t have anything (i.e., no knowledge).