Unnecessary Go Around
@Moloki and Silverstrata
You're both crazy.
The point is that there is an a/c on the runway when it shouldn't be and the tower was not aware. Who knows what was happening or what they would do next e.g. hijack, control issue, pilot incap.
What you are suggesting is handing your control over to the aircraft AWOL on the runway and cross your fingers that they figure their mess out before you impact.
The captain needs to always retain full control of their aircraft. A go around is always the correct course of action at any airport when you have aircraft not following instructions, in your immediate path and when the tower is unaware of the situation. Doesn't matter if this is BCN, Gatwick or the grass strip at the farm.