The question is based on this quote from Mahabharata (Vana Parva Section 115)
And grown resistless by the virtue of a granted boon, he ever mounted on that car, trampled upon gods and Yakshas and saints on all sides round. And all the born beings wheresoever placed, were harassed by him. Then the celestials and the saints of a rigidly virtuous life, met together, and thus spake to Vishnu, the god of gods, the slayer of demons, and possessed of prowess that never failed, saying. 'O blessed and revered lord, for the purpose of preserving all the born beings, it is necessary that Arjuna should be killed by thee.' And the mighty ruler of the Haihaya tribe placing himself on his celestial car, affronted Indra, while that deity was enjoying himself with Sachi, his queen. Then, O Bharata's son, the blessed and the revered god (Vishhnu) held a consultation with Indra, with a view to destroying Kartavirya's son. And on that occasion, all that was for the good of the world of beings, was communicated by the lord of gods; and the blessed god worshipped by the world, to do all that was necessary, went to the delightful Vadari wood which was his own chosen retreat for practising penances.
Did people start considering Kartavirya Sahastrarjuna a Rakshasa? Vayu Purana also labeled him as a good righteous king but Mahabharata says that he was a evil king. And if so, then why did not Visnu kill him the moment he harassed the Devas?