They’re bad guys because they murdered a bunch of families and young people minding their own business. They’re bad guys for weaponizing rape. They’re bad guys for knowingly bringing the wrath of the Israeli military down on Gaza. They’re bad guys for using money given to them by Israel and other nations to do those things instead of helping Gazans.
Note that I’m calling them “bad guys”, not “the bad guys”, because they don’t hold the monopoly on being bad. The IDF are also bad guys for their willingness to bomb buildings full of civilians for the chance of maybe killing a Hamas member or collapsing a tunnel.