Without a Sanhedrin you cannot have a torah society.
You cannot have a Beis Hillel/Beis Shammai Ellu V’Ellu situation
What happens if for example Rav Shteinman say what you did is Chayiv Missah and Rav Yosef says its muttar. Who is correct. It isnt academic anymore if the ability to carry out Skilah is done.
You need to have to same law for everyone