Any negatives?

Yeah. You can kill people.

When that stuff dislodges on the highway it's not like your car getting hit by a snowball. It's like having an entire wheelbarrow full of snow hit your car all at once at 50+ mph. Just the weight of it can KO your entire windshield. It's a super effective way to make someone crash.

Also, it's not always just snow. If the snow on your vehicle sat there through a couple of freeze/thaw cycles, there can be a big sheet of ice underneath. If that goes through someone's windshield it can kill them directly. If you live in a snowy place, pretty much everyone you know has a story about the time they almost died because some asshole was too lazy to clean off the roof of their SUV, or because a huge sheet of ice flew off the top of a semi-trailer.

Yeah, it’s wildly dangerous to drive with ice and snow on the top of your car as it becomes projectiles and hampers other drivers visibility.

In addition to what the others said, you're unnecessarily increasing the amount of ice/snow on the road. You also decrease visibility for drivers in the opposite lane depending on the wind direction. It only takes a couple minutes at the most to clean off the majority of snow, unless you're a lazy tosser.

A few years ago a piece of snow that had hardened from the cold flew off of the top of a guys car and hit my windshield so hard that it spiderwebbed. Snow flying off of a car can also completely blind you for several seconds, since it often comes off all at once like an avalanche.

If the snow suddenly obscures the vision of the driver, or a following vehicle, it's dangerous rather than annoying.

Given they're posting from lemmy.ca they're probably talking about the country they live in lmao

Crazy how you just assumed that they aren't canadian and that they don't remove ice/snow from their car, if they have one

Maybe in some parts of Europe, but this is illegal where I live. Punishable by fine or loss of license depending on how severe the coverage is.