While seriously irritating to those who PAID not to have SPAM, there is a reasonably effective way to avoid it. If you read the forum by using the "new posts" button, then this spam is easily recognizable just from the list poster names. Just don't open it.
I agree with Peter, we should all send our objections to admin. The material has nothing to do with Insights.
IMO, there is a bit of a dilemma here. Wrongly, many of us think that services and things can be free. Nothing in this world is actually free - someone always pays. Little doubt this is an effort by site owners to raise some revenue. We have no insight into how badly they need that revenue to justify their economic existence. It is being shown pretty consistently that the "free" internet model doesn't work, so they are trying something different. I deeply doubt that the small Insight community would support a "pay to play" site. JMHO as always.