Difference of opinion is one of mankind's natures, "And if your Lord had willed, He could have made mankind one community, but they will not cease to differ. Except whom your Lord has given mercy..." (Surah Hud:118-119) Doubtlessly, differences in opinion occur due to differences in intentions and purposes, differences in the strength of minds and perceptions, and differences in knowledge. Dealing with these differences requires a firm footing in the shariah.
Some du'aat invite to the unity of the rank and file in order to forget conflict, without defining as to whom to unify with and who to be separated from due to misguidance and deviations. On the other hand, there is one who exaggerates about the conditions, to the point that he wants people to agree with him in everything, even in his personal ijtihaad and his own opinions. And if anybody disagrees with him, he turns away from him, takes the attitude of resistance towards him, and becomes careless and disrespectful to him! Justice is accepting the difference in that in which difference is permissible. Like the means of da'wah, secondary matters, those rulings in which scholars of the past differed..., that which is based on the Shari'ah Ijtihaad in understanding of the texts, not simply on desires. As for leniency towards the people of innovation concerning 'Aqeedah, and fundamental deviations under the pretext of unifying the ranks, this is a false procedure that does not relate to reason nor to the shar'.
As for asking people to agree in everything, and not to differ in anything at all, this is impossible and unreal.