If I'm a responsible driver myself, then making myself and my family safe against the actions of other irresponsible drivers is totally rational and moral.
If someone is drunk driving in a Toyota Yaris and runs a red light and smashes into me, I'm not going to shed any tears that my big heavy SUV made it unsafe for them.
Even being a responsible driver you are still open to the edge case that you are going 45mph on a road that has a 45mph speed limit, doing nothing wrong, and a child steps out into your lane. Larger, heavier vehicles basically guarantee a fatality at that speed. The event was entirely out of your hands, well within the random risks of these events while driving, but your choice of vehicle has now made it a much more dangerous situation when it didn't have to be so dangerous. Pedestrians are involved in a minority of auto accidents but a majority of fatal ones, so if your goals are to decrease the risk of death in the general sense every time you go out on the road, you'd do well to choose the lightest and most sloping faced vehicle available to you.
It's basically a guaranteed fatality at 45mph in any weight of car - lots of towns/cities are even reducing their 30mph speed limits to 20mph for that reason.
If anything, I'd suggest doing 45mph on a road where there's the possibility of a child walking into the road faster than you could respond is irresponsible. If you're going that fast in a built-up area, you should either have a good enough view of the sides of the road that you can see the hazard developing in good time to react/break (ie, you're tracking the pedestrians alongside the road a hundred metres ahead of you), or you should be slowing down to a more appropriate speed for when you're lacking situational awareness.
I suspect this is a large part of the reasons that some countries (eg, the UK) have a hazard perception element to the driving test.
And by optimizing for the direct risk they are increasing the indirect risk by signalling to automakers and their government representatives that these are the vehicles they want to spend money on
Odds are the drunk driver is going to be driving a pick-up truck themselves [1].
This is a perfect example of prisoner's dilemma - everyone would be safer if everyone else was driving smaller cars. But because people are optimizing for their own safety everybody ends up buying large cars.
In the end, nobody is actually safer, and there are tons of negative externalities caused by everyone driving large cars (increased fuel consumption, road wear, significantly higher risks for pedestrians and other road users, etc).
If someone is drunk driving in a Toyota Yaris and runs a red light and smashes into me, I'm not going to shed any tears that my big heavy SUV made it unsafe for them.