Indeed. A forum is a public place and any opinions are welcome. Like any forum or blog, it is up to the administrator to remove non-related subject matter. Personally, I don't think there really is any problem. There are always some people on the net who post when they're angry. I've done it plenty of times.
But if anger is all that's there, and nothing is being said relevant to the forum, then the content should be removed, no different than if I tried to advertise my porn website on the forum.
Also, "ignorance is bliss" is a very old saying, one of those 'simple wisdom' sayings, like 'a bird in the hand is worth two in the bush'. Its been around for centuries. However that doesn't make it true. The individual decides whether or not it is true for him/her, and that decision is a reflection of that person's direction in life.