Rationalizing - what is it?
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 requires background in physics, chemistry and biology and involves creating and testing hypotheses. It 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.

Most people aren't challenged to reason effectively and "reason" only by rationalizing. This suggests that they employ Piaget's concrete operational reasoning rather than formal operational reasoning.

Effective reasoning requires careful attention to information sources. Scientific reasoning requires arguments to be supported by tested hypotheses.

Religion and politics often discourage thoughtful reflection and reinforce habits of rationalizing.
See Massimo Pigliucci on science education (pdf)

See also Chris Mooney on motivated reasoning