It's going to be really fucking difficult to make the Momotaro group even remotely sympathetic. They're genociding a race of people because they can go berserk and on a rampage - this is already an inherent trait within humans. Some of them go on rampages and kill dozens or hundreds of people. The only difference is that instead of using guns, bombs, or vehicles this group of people inherently have a weapon with them - their blood.
Like they're purposely killing innocents because they may go berserk and are doing fucked up shit to them and it seems that that's common knowledge considering how brazen they were.