What is the opinion of members about this? Is it fine allowing members here to promote or mention competing forums without paying this forum owner or taking his permission ?
it's fine, I mean I think even Theymos is fine about it, he mentioned that he tries to make the forum as free as possible(I assume that includes people advertising other forums). if you've been in the forum long enough you'll know come to find out that a forum called Cryptotalk.org that was owned by Yobit ran a signature campaign here.
The things on the forum which encourage spam are allowed mainly because it's part of the forum's mission to be as free as possible. Eg. banning bounties would undoubtedly reduce spam, but that'd be destroying an entire economy/population/culture which has been able to develop due to the forum's freedom. I am willing to take this sort of action, but only as an absolute last resort. It's always preferable to handle these problems by reshaping the environment to make them non-problems, rather than removing some freedom.
Yes, I know about cryptotalk.org. They failed to make any impact even after spending so much money paying users. Personally, I as a forum owner will never allow a competing forum to advertise on my forum though.