There are instances where you can run without a thermostat but a start and stop boat would not be one of them. Normally a restrictor plate is put in, in place of the thermostat. It almost every situation using a thermostat is far superior to not having one.
With out one it will cool just fine, like your friend said, but it will not warm up well at all. That means that you get less power, worse fuel consumption, and more engine wear. Because it's running without the temperature control you get less consistent power for starts and speed control.
Use a 160 degree replacement of good quality. If you had a cooling issue with lack of water flow past the thermostat you could put a 1/16"hole, or smaller, in the thermostat metal to the side of the valve. That ensures flow past it so it will open at the right time. You will be surprised how much longer it takes to get to operating temp with even a hole that size.