I do not think that there is anything wrong with putting ads on your forum. In fact, putting ads on your forum could be an incredibly great way to generate advertisement revenue. So, what are your thoughts about this?

If you do, don’t use the page takeover ad. It’s annoying and enough to make a person not come back.

There is nothing wrong in using ads on the forum but don't choke people with aggressive ad units that covers all the threads. You can use clean google adsense or direct sponsor banners that won't ruin mobile user experience.

Ads can definitely help cover server and domain bills once a community has steady traffic, but putting them up too early can hurt growth. If a brand-new forum is covered in auto-playing banners before it even has an active member base, visitors bounce immediately.

I think the cleanest approach is keeping the layout ad-free while you build trust, or only showing a couple of unobtrusive banner slots to logged-out guests while giving active contributors a clean reading experience.