Those who have life experience outside the DR should be able to employ common sense. If there are more bottoms than there are seats, if there are no seat belts, the only available space in the vehicle is in the trunk or the driver while approaching you demonstrates poor driving, you should be able to see the wisdom of not hopping on-board.
In this country, waiting for the perfect public ride will probably mean that you are standing on the side of the road all day. The locals don't have a lot of choice. They need to get to work on time or wherever they are going. It is a sad commentary that these public vehicles are usually old, in poor condition, overloaded and operated by someone who who shouldn't be allowed to ride a skateboard.
As a gringo, I am able to exercise a personal choice and I will not ride in a guagua or carro publico. I would rather walk, or ride a bicycle. I don't see a lot of people hitchhiking here, thumbs up and all that. If I was desperate I am sure that if instead of my finger to indicate that I need a ride from a public car, if I presented a 100 peso note to every private vehicle driving by, I'm sure wouldn't be standing there very long. Maybe not the safest of practices, but at least I would have my own seat and a seat belt. Probably working AC too...
As long as people continue to patronize decrepit missiles and the drivers of these POS can make money, nothing will change. I can't change the way things are but I am smart enough to know that the risks far outweigh the convenience or the expense of choosing a different option. I have that luxury and am fortunate in that respect. My level of life experience allows me to know with certainty that when playing Russian Roulette, everyone eventually loses. The better of two bad choices is not necessarily a good choice. It's too bad that the locals don't feel they deserve a safe conveyance and demand such from their officials in no uncertain terms. In the short term I choose not be be part of the problem by providing money to a driver that allows for one more unsafe trip from point A to point B.