Moving gameObject from A to B - unity3d

Question

I'm trying to animate / transform a gameObject movingObject from it's spawn position to the destination. I believe the issue is somewhere in the implementation of the IncrementPosition function.
Rather than moving the one cube from A to B. The script spawns multiple cubes until it gets to B. Can you see where I'm going wrong?
using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class onClickSpawnMove : MonoBehaviour
{
public float speed;
public GameObject randomSpawn;
private GameObject movingObject;
private Vector3 destination;
void Start()
{
Spawn();
}
void Update()
{
SetDestination(movingObject.transform.position);
if (destination != movingObject.transform.position) {
IncrementPosition();
}
}
void IncrementPosition()
{
float delta = speed * Time.deltaTime;
Vector3 currentPosition = movingObject.transform.position;
Vector3 nextPosition = Vector3.MoveTowards(currentPosition, destination, delta);
movingObject.transform.position = nextPosition;
}
void Spawn() {
Vector3 spawnPosition = new Vector3(10, 0, 0);
movingObject = Instantiate(randomSpawn, spawnPosition, Quaternion.identity);
}
public void SetDestination(Vector3 value)
{
destination = new Vector3(20, 0, 0);
}
}

Answer 1

There are several ways to call the Spawn / Start method casually:
gameObject.AddComponent<onClickSpawnMove>(); the Start method will be invoked again.
Instantiate a prefab that onClickSpawnMove script is attached already.
gameObject.SendMessage("Start"); maybe, but rarely seen.
You can add a log or break point to check when the Spawn / Start method is called.
Print the hash code will help you know the different onClickSpawnMove instances.
And you can click the message in the console to know which GameObject is.
void Start()
{
Spawn();
Debug.Log("Start " + this.GetHashCode(), this);
}