Smooth scroll with touch?

Here is a starter script. It has limitations and simplifications, but it something you can play with. Attach it to a game object with a collider. It assumes the camera is looking down the Z axis.

 using UnityEngine;
 using System.Collections;
 
 public class SmoothScroll : MonoBehaviour {
     public float fResistanceFactor = 0.98f;
     public float fStopThreashold = 0.01f;
     
     Plane planeHit;
     Vector3 v3StartPos;
     Vector3 v3LastPos;
     Vector3 v3Delta;
     float fStartTime;
     
     bool bTranslating = false;
 
     void OnMouseDown() {
         bTranslating = false;
         v3StartPos = GetHitPoint ();
         v3LastPos = v3StartPos;
         fStartTime = Time.time;
     }
     
     void OnMouseDrag() {
         Vector3 v3T = GetHitPoint ();
         transform.Translate(v3T - v3LastPos);
         v3LastPos = v3T;
     }
     
     void OnMouseUp() {
         v3Delta = GetHitPoint();
         v3Delta = (v3Delta - v3StartPos) / (Time.time - fStartTime) * Time.deltaTime;
         bTranslating = true;
     }
     
     Vector3 GetHitPoint() {
         Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         float fDist;
         if (planeHit.Raycast (ray, out fDist))
             return ray.GetPoint (fDist);
         else 
             return Vector3.zero;
     }
     
     void Start() {
         planeHit =  new Plane(Vector3.forward, transform.position);
     }
     
     void Update () {
         if (bTranslating) {
             transform.position += v3Delta;
             v3Delta = v3Delta * fResistanceFactor;
             if (v3Delta.magnitude < fStopThreashold)
                 bTranslating = false;
         }
     }

}