Rationalizing is the self-exculpation which occurs when we feel ourselves, or our group, accused of misapprehension or error.
James Harvey Robinson
"Rationalizing is a dishonest substitute for reasoning whereby we set out 'to defend our ideas rather than to find out the truth of the matters concerned.'... You are reasoning if the belief follows the evidence--that is, if you examine the evidence first and then make up your mind. You are rationalizing if the evidence follows your belief - if you'll first decide what you'll believe and then select and interpret evidence to justify it." - Source
Scientific reasoning differs substantially from rationalizing. It involves creating and testing hypotheses and incorporates peer review to reduce the influence of prejudice.
Rationalizing isn't usually intentionally dishonest, but rather it's a habit of thought within a social group. Rationalizing becomes apparent only outside the group where different rationalizations prevail or where reasoning is more analytical.