I actually thought overall the OP had some decent arguments. Yes Id cover off that semi auto isn't an assault rifle and is produced to be semi auto only so it's not easyto convert them to full auto.
Going with the car theme, I'd add that the semi auto is the street legal version. Not the race car track only version. Plus I would argue that a Ferrari has a double clutch automatic these days but why do you need to go faster from 0 to 60, or as already pointed out go over 100 km/h? I would then ask them what would they think if they bought a Ferrari with hard earned after tax dollars and a government then decided that due to single vehicle collisions, street racing and impaired driving deaths that they were going to prohibit your car or restrict it to track use only. You could only sell it to others with the same licence classification and you needed an authourization to transport to take it to the track. Plus you needed to belong to a track club or they won't renew your licence/give ATT. Add in Corvettes etc. The public would never accept this.
As for the "need" argument. I don't need more than water, food, and shelter. I don't need nice vehicles, fancy restaurants, a nice house, vacations etc. But then again I have no interest in living in a police state which is the entire premise of the "need" argument.
The AR was prohibited and then restricted based on the premise of "No legitimate sporting purpose". The irony is many hunters jumped on this bandwagon. What they ended up doing was restricting our modern day equivalent to the military Mauser action. The action that most hunting rifles are based on. The AR is able to group sub moa with ease, is light, very ergonomic can be free floated and based on synthetic materials. Everything you look for in a hunting rifle. The AR is prolific for hunting and varminting in the US.
As for the hunting argument. People that argue this don't seem to understand that it is more humane if a follow upshot is required. Plus dangerous game hunting. Wild boar hunting etc can be very dangerous for the hunter. A semi auto can be the difference between life and death for the hunter.
Also for "hunting" these people aren't aware of varmint hunting. Farmers often have to contend with prairie dog colonies etc. An acurate semi auto such as the AR15 can be very sucessful for this. For farmers getting rid of a threat to their crops, livestock etc isn't sport. They want to tackle this quickly and efficiently so they can get back to farming. Same goes for Coyote problems or other predators which threaten livestock.
One last point I like to hit on. These semi auto military based rifles are coveted possessions. They can cost anywhere from $800 to over $3000 without optics. They are secured by owners the same as any other valuable. They aren't just left around as their cost and pride of ownership put them in colectable/coveted possession territory for legal owners.
Ultimately we all know the anti mentality is a foot in the door method. It will never be enough. Tomorrow handguns, then those Mauser based "sniper rifles" many hunters hoped were off limit. In a perfect anti world your only weapon is a phone so the state can protect you. The extreme right and extreme left both have one thing in common. They ultimately both lead to a police state. Everyone knows what's best for you and everything is for the good of the state. Just think of the children! A tried and true way of giving up ones rights and freedoms. The "need" argument is the foot in the door/slippery slope to this. It's especially easy to justify this when taking away rights and freedoms from a minority. Another age old tried and true method. Obama has recently used both of these tricks.
