is it permissible to join a group chat for permissible matter but there are sins in that group?. For example, there a facebook group for selling bicycle stuffs, but there are people who use human images as their profile picture, or someone who post forbidden pictures.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is nothing wrong in accessing websites or groups whose purpose is principally and mostly permissible, even if some forbidden images – or similar things that should be shunned as per the Sharee‘ah – are sometimes displayed therein, as long as the visitor’s intent is to benefit from the website or group in what is permissible. The visitor, however, is required to lower his gaze from (looking at) forbidden images. This is because such evils are widespread nowadays in a way that makes it hard to avoid them, and Muslim scholars established that hardship entails facilitation.

Moreover, such forbidden contents are not the main target of the visitor or creator of the group, and the rule is that subordinate matters may be pardonable unlike principal ones, and that it is possible to judge some matters as valid when they are subordinate, while they cannot be judged as such when they are independent.

As-Suyooti said in Al-Ashbaah wa An-Nathaa’ir: “Pardon is acceptable in that which is done as an implication, but not when it is intended in and of itself.” [End of Quote]

Allah Knows best.