"they want you to install a Search Hijacker App from Google Chrome" Sites like Adfly and Shortest do not do that. Maybe the people paying for ads on their sites are, but not them. Should sites like Adfly have stricter rules on what advertisers can advertise? Yes. But I guess they have to make money somehow. Also, it's not like you have to install anything to get to what you want to download. Just click the Skip Ad button.
Link shorteners with ads is the main way a lot of creators on this site make $. If these link shorteners are banned, there would be a lot less motivation for these creators to make content. And this causes a cycle of less content being made and due to that, less people on the site.
