Hmmm, I'd say socialism itself got corrupted over time. The french socialist party hardly can call itself socialism in this days lol... Even though I have to say I agree with it's actual position.
And yea, you can stop at socialism if you want, many "communists" that took power couldn't move or didn't want to move to anything past that.
For a lot of socialists, communism is not and never was the goal. Case in point; Hitler, who absolutely hated communism.
Like I said, Marxism is a very specific type of socialism, one which intends to implement communism.