I'll take a 3 ton vehicle over a 1 ton vehicle any day (if that's your only issue)--you just can't mess with Newtonian physics.
You can't mess with responsibility either. But let's be strictly scientific first, and talk about physics (I'm a physicist :wink

. There are several safety drawbacks in high and heavy vehicles, like roll-over or braking issues, but to make arguments more accurate you must distinguish two cases : collision with a fixed obstacle (tree, rock, wall...) and collision with another (usually moving) vehicle.
- fixed obstacle case : a larger weight does NOT give you any safety benefit. What only matters is how smoothly the vehicle can make your body decelerate from x MPH to zero MPH, thanks to a proper (car) body design, airbags and so on. In other words, how gradually the vehicle can dissipate kinetic energy. Most off-roaders are worse than regular cars on this point, because they need a very stiff chassis for off-road purposes, and this chassis does not allow enough deformation in case of a frontal impact.
- moving obstacle case : as you probably know, there is a law in physics called momentum conservation. To illustrate it in a simple way, let's take two vehicles moving at the same speed but in opposite directions. Consider the heaviest one is moving from the left to the right in front of you, whereas the lightest one is moving from the right to the left. Because they have different masses, there is a non-zero momentum of the whole system made of the two vehicles : this momentum can be represented as a vector pointing in the right direction.
Then the two vehicles collide frontally; just after the collision they can be considered as one mass (instead of two masses having different positions before) and because momentum is conserved, this mass is still moving to the right, until friction stops it. In other words, although the two drivers were moving at the same speed before the accident, the driver of the heaviest vehicle will experience a less brutal deceleration, just because he transferred a part of its kinetic energy to the smaller vehicle.
Some people can use this argument to justify driving a heavy vehicle even if they don't need it for towing a trailer or carrying some heavy stuff. I just think the absolute opposite, and would advise these people to try psychoanalysis in order to understand why they don't feel any compassion for their human counterparts.
Physics is not the only part of the problem.