The tradition where most users of this forum started from; alts are typically used to say anything controversial, report cheaters, especially for people who don't have the courage to use their main account or don't want such reports/statements to be tied to their main account. Now you're asking those people to declare their alt accounts in public.
I see no reasons why Alt account shouldn't be allowed for those who intends to use it properly.
The problem with reporting cheaters on the forum you mention is that scam is not moderated there at all, so everything is based on public investigations of regular users. Unlike that anyone can report everything just using a Report to moderator link under the post. If you understand that forum staff can detect your multiple accounts, why not to report from the main account? No real reason.
As for public declarations: no, no one forces anyone to declare alt accounts in public. You can do it privately and only admin and the President will know, even GMs will not, all will just see some account with a corresponding badge, no one will know whose this account is.
And about saying something controversial: altcoinstalks is a friendly forum. If you think that what you say leads to misunderstanding and aggression, better not to say that, IMO.
So no, I see no reasons to allow multiple accounts. Moreover, all multiple accounts found recently were used for shilling, scamming, spamming or participating in paid campaigns of different sort, no single caught account was used to report bad actors or just to say something controversial.