Whay turbocharged engines have oil coolers?

I have a Volvo Penta 2003T engine in my 1992's 36 ft sailboat; this
a turbocharged version of the 2003 and it have an Oil Cooler
instaled inline, before the fresh Water cooler. The oil cooler is made
of aluminium with the inner tubes of cooper, and because it uses raw
water, is prone to corrosion. A new one, woul cost to me, here in
Brazil, about US$ 1,200.00 wich I think is unaceptable.

This engine is 45 HP, and has a turbocharge (turbine) but the
operating temperature is not so high; the thermostat begins open at
74 °C and is fully open at 87 ºC; the new Volvo Penta 2040 wich is
not turbocharged and has 40 HP, operate at a higher temperature
(82-95°C) but does not have an oil cooler. Both engines uses the same
lub oil (15W40).

The oil cooler, is a very critical piece, since it can cause the
complete desctruction of the engine, in case of the raw water goes to
the engine lub oil. I am tempted to eliminate this oil cooler
bypassing it and not refrigerating the lub oil at all. What would be
the drawback? I use this motor very lightly, at 2,000 rpm, not at
the maximum 3,200 rpm.

Thanks for the help

Pascal Goncalves
Salvador-BA-Brazi