Having multiple accounts is not an offense by itself on this forum. If you encounter a negative trust rating with such an explanation, it is a sign of misuse of the trust system. (I honestly didn't notice such trust ratings from DT members based on multiaccounting. Perhaps you have some example to show?)
I haven't seen any DT member giving negative trust to someone just because of using multiple accounts. But the trust system has been used for giving negative trust to users who use alternative accounts for cheating in bounty/signature campaign, ban evasion or abusing the merit system. That's probably what OP is referring to.