Incentives are powerful, and typically get the result they are incentivizing in the end. All taxes are a form of incentive, we should always be careful of taxing things that we want more of.

If you favor a wealth tax, you are implicitly arguing in favor of incentives to create less wealth. If you tax investment, there will be less investment. If you tax the rewards from great risk taking, there will be less great risk taking. So every tax is a trade-off: are we better off with less of the thing we're taxing and more in the hands of whomever is collecting the tax?

A related point would be that wealth can be created from nothing. It is not zero sum. My sense is that many people advocating for a wealth tax do not understand this conceptually.