Shirou's logic is your typical villain's bogus logic - in the same speech, he complains the powerful impose their will on the weak and calls it a "twisted system", yet in this story he is "the powerful", and humanity is "the weak", even if his goal is fundamentally benevolent.
I guess all bad guys are doomed to be hypocrites at some point?
Also, poor Semiramis getting trolled by Achilles like that.