Ok I understand the difference in grounding and bonding... And everywhere I read it all says NOT to connect the bonding system to the grounding system of your house... But, the NEC requires a #8 insulated wire be run in the light conduit to the deck box... This wire gets tied into the grounding system of your house.... On the light niche there is a lug to which this wire connects.... On the outside of the niche is another lug that the bonding wire connects to.... BUT, these 2 connections are tied together with a small metal plate.... So now, if everything metal is bonded together it is now grounded through your house grounding system... Right? And if so... Why is it such a big deal if people run it to, say, the ground rod of the house?

Hmmm... everyone told us that we SHOULD run the pool bonding back to the house earth rod. That's what our sparky has done (via the earth wire in pump GPO).

The rule in Canada has always been to ground the bonding system. In the US the old rule was to never ground the bonding system. That was then changed to say to never intentionally ground the bonding system, and then changed again to allow grounding the bonding system. In practice the bonding system nearly always contacts the grounding system at some point, typically at the pump and in the junction box for underwater lights, and there is no easy way to avoid that even if you wanted to. Everyone who stresses never connecting bonding to ground is working from the older rules.

There are very very small risks with either approach, and it appears to be impossible to come up with any approach that is perfect. If the bonding system is connected to ground you have one or more ground loops, which can cause the wiring to fail sooner than it might otherwise. If there is no connection, there is a secondary risk from the bonding system getting shorted to a live power wire without tripping a breaker. That isn't a risk to a swimmer but can be a problem for people stepping off the deck or touching the pump/heater.