Although I agree with you on the due process, you basically have to live in the Philippines to understand why it has taken this route in solving a long standing problem.
It's the same thing how we tell other people from other countries, who make comments about our gun problems here when it is not, but they don't understand because they don't live here. Hell, even people who live here don't understand it.
The current problems the Philippines are dealing with is beyond solvable through civil means, many Presidents have failed and the people are tired of the crimes and the corruption.
Duterte's ways were proven effective being a mayor in a city so he implemented it nationwide.
He's got a huge burden on his shoulder right now because that's a huge amount of **** that needs to be removed in that country. Now he's also dealing with muslim extremist in Mindanao, whom are also a long time problem.
Also, their prison system is so overcrowded that you can call it a can of sardines.
I've lived there for 23 years and grew up in the slum area and I see it while growing up. I go back from time to time and seen improvement over the years. A couple of friends just recently went back and already seeing progress as he took office, especially on the curbside sanitation.
I can honestly say that this guy is actually doing some real work. And he's got 6 years of hardship ahead of him in tackling a mold that has gripped that country for decades.
While I certainly respect your point of view, it's incredibly difficult, regardless of the benefits (in my mind), to justify summary executions of not only drug dealers, but users and addicts. It smacks in the fact of ones natural rights.