You need to ask the correct questions to get the correct answer.
Why are the Democrats so concerned about him?
Hint—it is not “issues” at all.
It is exposure.
RFK Jr. will get exposure (good and bad) on mass media sites that are viewed and trusted by Democrats and Democratic leaning independents and despised and distrusted by their Republican counterparts.
The Democrat professionals understand this.
Given my understanding of his stated positions on various issues I can see the "undecided" seeing him as the least evil/worthless/inept of the three main candidates.
As I said before I hope to God I'm wrong...and I certainly could be. I was wrong once in 1982!