The country is likely to be in a state of turmoil over the fact that their president is claiming murder, and now is probably not the best time to be holding a concert. A concert might be appropriate in the future, but at the moment Taylor is wise to cancel his concert.
I don't know enough about Duterte and the overall situation, but the extrajudicial killings are scary. Duterte claims that if innocent people are killed, it's not a crime, and he's not going to stop. Getting the war on drugs under control is a good goal, but it seems that plenty of the Philippine people are afraid of Duterte and getting killed, so I don't blame James Taylor for backing out.
Extrajudicial killings under the Duterte's Government need to stop. James Taylor did the right thing by canceling his trip. Maybe if other performing artists and companies start to boycott the Philippines Mr. Duterte will start to feel some pressure. The pressure from his citizens is not working. It may take outside pressure to get his administration to stop the killings.
Duerte has demonstrated that he is a violent dictator of sorts. His brutal remedy for illegal drug trade has rattled the world. It can be argued whether or not his methods are improving the drug problems but I think time will eventually prove that Duerte is a monster acting on fears.