> whom they propose to give that power of appropriation, and why they trust them to use it wisely.
Existing state structures, through taxes/subsidies/government expenditure/laws/regulations, already redistribute wealth from some socioeconomic classes to others. These structures are to certain extent decided by elected officials and somewhat by other big players (eg. bank regulations on overdrafting).
Degrowthers are asking that society elect officials who make the economic changes they want, which they are legally empowered to do. Since, the overall system is not being changed, I am not quite sure what your concern is.
> Did those forms of socialism create just societies or enact massive violence against humans and nature?
Please understand the difference between democractic socialism and Marxism (and its failed implementations in the USSR). Various forms of democratic socialism are practiced across Europe and Canada and they are not particularly known for massive violence against their own citizens.