I was a CTO of a company that did scraping to gather data and sell the analysis. We did this for sellers on Amazon.

In short about legality - it depends on the country. But most will define user content as owned by the user, not the platform, therefore legal to scrape and use, as the user intents for the data to be public.

But sites will fight you on this. Amazon specifically give up a really good fight.

Ofcourse, this talks about user content in an "open" platform. If the content is owned by a business that has no intentions for it to be open for everyone in every medium, its probably illegal.

In regard to being a dick move, it depends. If someone posted an ad in facebook, he intended for it to be seen. He doesn't care how. I just tunnel it to myself in easier way for me to consume.