I'm not sure the comparison is entirely valid, but in condemning the "brutality" with which Assad is suppressing the rebellion in his country, we might want to reflect upon the fact that The United States was not exactly restrained in the manner in which we suppressed rebellion in this nation. Sherman's march to the sea was hardly an act of kindness, and he burned Atlanta to the ground. Vicksburg and Shreveport were shelled for weeks without discrimination. We thought then, and continue to think now, that such action was justified in maintaining the integrity of our nation.
We may not consider Assad to be legitimate, but he does; and he still enjoys considerable support in his country. What is he supposed to do about those who are trying to overthrow him by force? He is meeting force with force, admittedly with greater force, and I'm not sure that he doesn't have the right to do that.