The big problem with them is that usually there isn't a single kangaroo to try and dodge on the road, but several at once. The recommended course of action upon encountering a roo on the road is to just keep driving straight. If you try and dodge it, you're just more likely to crash your car and just as likely to hit a kangaroo. They're big enough to cause a lot of damage to a car too.
They're absolutely a pest, and there are unnaturally high numbers of them from eating crops. Culling keeps the population down to healthy numbers. I think that most opposition to culling is because they're Australia's national animal. Nobody complains about culling foxes and goats. I also don't see how culling is any less ethical than farming cows or sheep.
Also, this is an interesting quote:
> There may be no animal and nation in the world more closely identified.
I'd argue that New Zealand and Kiwis are much more closely identified, to the point that New Zealand and Kiwi are literally synonymous. If someone asks me what nationality I am, I'd say "Kiwi" before I said "New Zealander". Never heard an Aussie refer to themselves as a roo.