Inheritance tax in practice is implemented above a certain threshold.

There is nothing wrong with striving to give a heads up in life to your kids, on the contrary, it's a core, visceral instinct of parents to do so, and removing that would be alienating.

There is a certain level of wealth though, where the "heads up" transforms to an unstoppable compounding lever.

France for instance has a progressive inheritance tax (starting at 5%, up to 45%), triggered for children inheriting at 100k€ per parent. In practice, 50% of the population inherits <70k€.

Also, the proposed Zucman tax in France for instance is triggered starting at 100M€ wealth. At these levels, a mere 2% risk free investment yields 2M€ annual income, this is enough to both compound and enjoy a very luxurious lifestyle. This level of wealth is unstoppably compounding, and that is why it is proposed to tax it.

If you don't, well you end up with a US situation, where disproportionate wealth (and thus power, influence) end up in the hands of random citizens with their own agendas, possibly (likely) orthogonal to the interests of the majority.