If you are using our CBC or ACBC software and if the utility estimation settings are at their default, then the raw utilities within attributes are indeed zero-centered. The rescaled utilities (zero-centered diffs) coming out of all our conjoint systems (including ACA and CVA) are also zero-centered within attributes.
But, a negative doesn't mean people feel negatively about a level. It just means they have relatively lower preference for a level relative to the other levels within the same attribute. All levels in reality could be positively viewed; or on the other hand, negatively viewed. It's just that some levels are relatively preferred more than others within the same attribute.
Standard conjoint methods do not have a way to measure if all levels are disliked or liked within an attribute; only the ability to estimate relative preferences within the same attribute.