If there are a lot of alt account then we have no problem or we don't have anything to be worried about until it breaks any rules of the forum. Until it spam on the forum, it tries to scam of the forum members.  Or regarding bounty until it break the local rules of the bounty.

Considering alt base on ethereum transaction is worthless. Because the transaction may happen with friends, relatives, and also it can happen for buy/sell/exchanges.