When people talk about wealth inequality as a bad thing they're normally talking about self-perpetuating wealth inequality, or wealth inequality that is caused by things that are seen as inherently unfair, like the family you are born into.

A lot of people who have comparative wealth and have worked hard for it feel they have earned their wealth, disregarding the fact that a lot of other people work equally hard and do not have the same amount of wealth. This sort of thing muddies the issue.

Also muddying the issue is the fact that some people think that if X amount of money could lift Y poor people out of poverty, vs making rich person Z marginally richer, it is self-evidently the case that it is better and therefore right for X to be spent on the Y rather than person Z. I.e. as long as some people are below a minimum acceptable level of wealth, all wealth inequality is, in this view, bad.