Being objective is as important as being accurate. It's a matter of fairness. Interjecting personal opinions into the ideas or information in your summary confuses the reader by obscuring the information in the original source material. Expressing your attitude toward it, whether negative or positive, is inappropriate and self-serving.
You may express your own opinions, of course, but that should be done in the surrounding comments framing your summary. Bear in mind, being respectful is simply a matter of good form when arguing a difference of opinion.