I don't blame you for having reservations about that. In fact, conventional modern motor oils are very good, and they are considerably better than was the case 20 years ago.
However, a bit of research will reveal advantages of synthetic oils:
- Better resistance to breakdown under prolonged heat or overheating (great protection for the engine if you have a thermostat lock up or a radiator hose blow)
- Better wicking throughout the engine, including on the bearing surfaces that are exposed to wear at cold starts (a benefit at every start)
- Better resistance to film breakdown under high pressure at metal-to-metal interfaces
- Polymer chains that hold up longer under extended service, preserving the oil's ability to maintain proper lubrication (making it easier to extend change intervals)
There are other reasons, but these suffice. Aside from marketing blurbs, I've been reading oil tests for 30+ years and at least for me, the evidence is sufficient.
The exception I've made to running full synthetic oil was to run a synthetic blend in my daughter's '91 Camaro, which used about a quart of oil every 1200-1500 miles. I thought the blend was a good compromise, and that engine ran nicely for the seven years she owned it, still running great at @165K miles when we sold it.