I have lived at the coast all my life and spend a lot of time fishing at the beach. Recently I read an article about the damage that 4x4's do to sand dunes and now I am conflicted about taking mine right onto the beach. I don't know whether I should stop driving onto the beach altogether or whether there is a way of doing it so that I don't contribute to damaging the dunes. Any Advice?

In my view, there are three issues involved with beaches and sand.

1. Fluid spills. Oil, gas, and antifreeze are noted pollutants. So, keeping your vehicle right side up and in good maintenance should reduce that risk.

2. The sand dunes. The dunes have significant plant vegetation that helps stabilize the dunes. Driving over the vegetation does break down the stabilizing ability of the root structure.

3. Low to high tide zone. Driving within the low to high tide mark does contribute to compaction and there are numerous shell fish that inhabit that area.

My belief is that as long as vehicle traffic is in the open sand area, above the high tide mark and out of vegetation, minimal damage is done to the beach.

Most of the CA coast is closed to Offroad vehicle use now.
Many reasons for this as stated above.
We have an area set aside for ORV near me, Oceano Dunes State Park. It took about half the range of a lizard that lives nowhere else. This areas microfauna will never recover untill after the next ice age. There is an issue with sand being ground up and blowing to a nearby town,that has treatened to close it and/or have strickter regulations place on it. It is a very heavily used park. I hope they keep it open,,,even though I don't run my rustfree Montero there ( I'm a ridgerunner).

I suppose if the damage is already done, then it would be stupid to close the area to off road vehicles, but I do think it was unresponsible to kill off half the poor lizard's habitat just for driving off road.

I think I will go driving on the beach, I'll just make sure I drive on the unihabited areas.

Yes ,it was very unresponsible to destroy the habitat. That was done before most folks cared or knew any better. Unfortunately we clearly know better now but this still continues too many times for short term fun or profit.