Would it not take lot more effort to stall a PPG, loaded over the gliders weight range?

I'm glad you asked, since apparently many pilots have a misconception on this concept.

Any wing stalls because you exceed it's critical angle of attack. The angle of attack that the wing stalls is the same regardless of the weight, but the speed at which you will reach this critical angle depends greatly on the load the wing is required to carry.

Angle of Attack is the angle between the chord line, and the relative airflow. If you need to support more weight, you will need to increase the lift, which is done by increasing the angle of attack. As you need to support more weight the stall speed will increase, making it easier to stall the wing when it overloaded.

In case you care, the stall speed increases as the square root of the wing loading. For example if your wing stalls at 15 MPH and you maintain a 60 degree bank turn, the wing loading doubles (your are pulling 2 G's) and the stall speed increases 41% to 21.15 MPH!

Herein lies the root of the dreaded downwind demon... You take a heavy pilot on a wing that is to small for them, so they will reach the stall point at a higher speed, then wank it into a turn close to the ground. Compound this with the illusion of increased speed by turning downwind close to the ground and add a wee bit of brake subconsciously and WHAM! You smack the ground before you can say Oh @*^$!

Give the same guy some altitude to recover from the stall, and they might get an uncontrolled surge and fall into their glider. Straying outside the certification placards is a recipe for an interesting flight if you get a collapse.

Now the advantage is in turbulent conditions that the wing is much less prone to collapse with a higher wing loading. I personally believe in flying a glider that is easily big enough to support the load it needs to carry under all conditions. Sure it takes more work to ground handle a bigger wing... that's what ground handling practice is for. Give me a rough day, and I feel very confident on my big fat wing that holds lots of air, and is frankly not terribly prone to deflating anyway...

In short, and generally speaking: a heavier loaded wing will:

1. Be less likely to collapse.
2. Recoveries will be more dramatic/quicker/severe 
3. Higher airspeed/landing speed/stall speed.
4. Quicker to roll into turns

A lightly loaded wing will:

1. Be more likely to collapse
2. Have a softer/slower recovery
3. Slower airspeed/landing/stall speed
4. Slower to roll into turns

I agree totally, but I would add that a lightly loaded wing, while more likely to collapse will collapse with less severity than a heavy wing. I have tried asymmetric deflations on my tandem with and without my motor, and it is almost boring without the motor, since they are so mild. I do fly a tandem glider, and it holds a lot more air (mass) than a smaller wing so this may not be particularly representative of what happens with a tiny wing.