I think if your goal gaining more members and being more popular in SEO, making your forum private is a bad decision. Allowing your forum to be a public one would not only be more accessible to curious people or interested to be new members, I believe it would also be more friendly to SEOs because it'd be easier to generate traffic. If you make it private, it'd be harder to find new members and it would be far from accessible. I think if you do this, you'd lose not only profit, but also your present popularity.
I am currently running a forum. There are some threads/posts that are not viewable by the public and others that are. In order for say Google to crawl and your SEO to work, something's need to be seen by the public. So a completely private forum would not work well in my opinion.
Good Luck to You.
I really agree on this and if the goal is to earn more money and have more followers, making the forum private would be the complete opposite of what has to be done. I also believe that SEO can really help a forum become more popular and visible to users, and in order for the website to be SEO friendly, it needs to be seen in public.
Yes, but if the goal is for it to be SEO friendly and have more followers, I think putting it in private will do the complete opposite. Most people who become forum owners do it to earn money while sharing their views and opinions to other people. I don't think it's merely to just to be able to say whatever you want online, thus, it's necessary to have many visitors on the website and for the to happen, it has to be publicly seen.