Having seen the orderly arrangement of things on bitcointalk and how matters of scam are taken very seriously, I think there is no need for more forums because the more forums we have, the more likely scam activities in the crypto-world will occur. Of all the forums I have seen, bitcointalk is the only one that has a measure to fight scam. The rest just take fees and promote projects on their forums without any checks. (On bitcointalk, we believe everyone has the power to take action when a project seems to be a scam for the higher members of the forum to work on.)
I understand that blockchain and decentralization move together and for that matter, more forums for cryptocurrencies discussion should not be a big an issue but with the recent scam projects ongoing, my opinion is the leave everything in the hands of one forum to handle all ICOs discussion there.
i think Bitcointalk is the best cryptocurrency forum in the crypto community. This forum has many experts and experienced individuals of cryptos. So their experience and knowledge is useful in phishing out fake ICOs.
But as we seek to expand the crypto sphere, it is important to have other forums because some people that may get access to those forums may not get access to this forum. Just like some Altcoins, some crypto forums other than Bitcointalk may be useful to the growth of cryptos.