The idea of don't swerve for deer is very common and is taught in driving schools. If you've never heard it until today, well you were let down and today you learn. You don't know dismiss it because you haven't heard it.

Swerving is dangerous and even if you think you can do it safely, having a deer appear while travelling at high speeds is risky, even more so at night.

You're supposed to slow down but stay in lane.

The reason you're supposed to swerve for things like Moose is because moose are big as fuck and tall, and if you hit one head on, you will cut the legs out from under it, and it's massive body will roll through the windshield and crush you, killing you or causing massive bodily harm.

This is from the Virginia DMV for example (emphasis mine). Them not having something about moose is actually bad as well.

https://www.dmv.virginia.gov/sites/default/files/forms/dmv39d.pdf

Deer/Large Animal Hazards Tens of thousands of crashes with deer, elk, and bears take place in Virginia each year, resulting in fatalities, injuries and costly vehicle damage. To avoid hitting a deer or other large animal:

• Be alert at dusk and dawn especially in the fall.
• Slow down if you see a large animal near or crossing the road. Large animals frequently travel in groups; there are likely others nearby.
• Use the horn to scare the animal away.
• If a collision with a deer or other animal is unavoidable, do not swerve. Brake firmly, stay in your lane, and come to a controlled stop.