It's not a matter of justified or not; morals had little to do with European exploration. Most of the shortcomings of European exploration were due to a lack of understanding of the native people and a lack of diplomatic relations, a term which natives were unable to comprehend. If I had to answer, European exploration was justified since there was no reason NOT to explore the far reaches of the unknown and because Europeans were civil and did not seek to mass murder every native they found. They had no idea that their diseases would be so devastating since medical history hadn't gone that far. From their point of view, they didn't think natives were civilized and yet attempted friendly relations anyway.
