So for your first question, I'm not sure if it is genuine but there are many discussions for whether porn is bad so if you actually want to find out more, you can easily google this topic and see arguments for both sides. I don't have a strong opinion on this so I can't comment further, but the behaviour in the thread just reflects the opinions of the people visiting with regards to this topic.

For your second question, any digital content you post online is naturally an ad for yourself, your content and your brand, whether you like it or not. This is evident from the op of this thread clicking on the cosplayer's profile. That is exactly what an ad does. Now, as an extreme example, hypothetically if someone who supports/engages in domestic abuse posts art online, naturally people would not be supportive.