It depends on a lot of variables.Chile is pretty safe i believe.They are used to boaters on the Zambezi ,so besides hippos and crocs ,your main danger is pretty crime off the river.If you go somewhere like Somalia, or until recently Columbia,kidnapping is a potential problem.If you are running some remote river in a developing country the locals may suspect you of scouting for some mining or dam building company and apprehend you.This happened on Rio Copon Gt.a few years ago.Bandits were attacking rafters on Rio Usumascinta in the past.
I want to explore the upr.Chiquibul river in Guatemala near the border with Belize.The run has been done a couple times and is mostly 2-3 with some 4 and a couple portages.You have to carry in an hour or two.The river is a tributary of the Mopan,which I have run many times.I have followed the explorations of Rocky Contos for years.He will run a river from it's headwaters all the way to the sea,V to flatwater.This idea appeals to me ,and either the Chiquibul-Mopan-Belize River or the Chiyu-Gracias a Dios-SanPedro-Sarstun are basically the options i have narrowed it down to without getting in over my head whitewater wise.Both of these involve traversing Guat-BZ border areas where there are serious disputes.The Guats don't acknowledge/respect the border.They claim Bz is part of Guatemala.There is transborder:illegal gold mining,poaching plants and animals,looting archeological sites,peasant farmers squatting on the Belize side,and human and drug trafficking.Belize has too little law enforcement resources to do anything about it.The people who are doing this usually live in the villages just inside Guatemala,like the one you use to access the put in trail. for the Chuiquibul.I would hesitate to hike in here alone and come across these folks but if you hired some porters to guide you in and carry your stuff you would probably be fine once on the river.But it is dangerous.
I dreamed of exploring Michoacan in the past.Rocky did few rivers there.I googled one of the rivers he did for pics and a bunch of images of decapitated bodies came up.There are State Dept.warnings against travel in Michoacan,Guerrero,Sinaloa,and couple of other states.I saw where some guy on team Jackson bagged some 1D's in Michoacan a few years ago anyway.There are reports of tourists getting caught up in cartel violence,but it is rare.Compare a handful of incidents to the millions of people who visit Mexico annually.Outside of border areas and drug production areas you are still relatively safe.If tourism is an important part of the local economy all the better.