Killian Jones, the person who knows and understands Emma Swan better than ANYBODY ELSE, knew she would react the exact way that she did. He understands what his ‘leaving’ would do to her. How it would hit her and what she would do (remember how he asked her not to put her armor back on when she was leaving him in the Underworld? He KNOWS her).
Killian Jones isn’t thinking less of Emma, and I don’t think it’s fair for anybody else to do so either.