Being in the group chat when it happens can make you part of the screenshot.

A conversation with twelve people in it is a document, and documents get forwarded. Presence gets read as agreement by anyone looking later, because a screenshot does not show who was uncomfortable and saying nothing. That is a harsh way for it to work. It is also how it works.

If a thread turns into something you would not want attached to your name, you can say one flat line and stop replying. Leaving is also an option and needs no explanation. Silence inside the chat is not the same as distance from it.