A typical response to this issue is "why does it matter to you if someone else has more than you do?" - framing the issue as essentially envy. The obvious problem here is that it really is largely a zero-sum game. A dollar represents a claim on the world's resources, which are limited.

Capitalism is an effective system for motivating productive activity, but it also has an inherent tendency to concentrate wealth.

If we want to avoid a situation where a few people control such a large proportion of the world's resources that there is not enough left over to meet the needs of others, then we need to balance this tendency. Income taxes are one approach, but wealth taxes deal with the actual issue.

Taxing wealth is not unfair if you accept that the economic system we have chosen is itself unfair. We give too many advantages to those that gather income through owning things (i.e. unearned income) compared with those that engage in productive activity (i.e. earned income).

I say we 'give' those advantages because they are not due to some inherent law of nature. It is a choice we have made as a society. In the natural world hoarding works in the opposite way. A stash of nuts doesn't magically grow. Quite the opposite. Real effort has to be expended to preserve the stash.