Lots of people think that a few people controlling a very large share of a society's economic power is a bad thing. It is unfair that some should have so much while so many have so much less. It is inefficient that so much wealth lies in the hands of people who already have everything they could reasonably desire.
It is inefficient that so much wealth lies in the hands of people who already have everything they could reasonably desire. It gives some people an outsized influence on decisions that affect the whole society, and on democratic politics itself (previously). These people often also worry that economic inequality is increasing and becoming entrenched as the rich pass their excessive wealth on to their children and more and more wealth ends up concentrated in ever fewer hands.
These people often also worry that economic inequality is increasing and becoming entrenched as the rich pass their excessive wealth on to their children and more and more wealth ends up concentrated in ever fewer hands. Many of them think increasing inheritance tax is necessary to stop this.