You can’t really judge Sisi except in terms of the situation that brought him to power. Although Muhamed Morsi, the Muslim Brotherhood candidate, was elected President of Egypt after the overthrow of Hosni Mubarak, one of Morsi’s first actions in office was to issue a “temporary constitutional declaration” which suspended the constitution and gave Morsi unlimited powers and the right to legislate, without judicial review of his actions. He then appointed an Islamist dominated constitutional assembly to draw up a new Islamist constitution, presumably to be based on sharia.
Moderate Muslims, Christians, and liberals were appalled at what they considered an Islamist coup and soon demonstrations broke out demanding that Morsi resign or that the army overthrow him.
As we know, the Army, under General Sisi, did so.
The Rabaa massacre developed when Muslim Brotherhood supporters protested the coup by staging massive sit-ins, the largest at the Rabaa al-Adawiya square in Cairo. Demonstrators set up barricades, a wall to slow armored vehicles, and, when police moved in, resisted violently and were reinforced by people moving in behind police lines.
While details of the incident are controversial (the government claims that the demonstrators were armed and fired on police,) it is clear that the demonstrators fought back, and that the incident precipitated Islamist violence across Egypt.
While Sisi’s human rights record has been dismal, so were the records of his two immediate predecessors. And it isn’t clear that the Rabaa massacre was solely the fault of the new government. Compared to the “Saudi led coalition” fighting against Yemen, the Israelis periodic “mowing the grass” in Gaza, the US coalition in Libya, all the sides in Syria, Sisi is a regular teddy bear.
Egypt is one of the most important countries in the Arab world. The US has to have a strategic relationship with that country.