The short version of the SE-can't-tow limitation: It's a software issue not a hardware one.
Mechanically it has the exact same capability as the other models.
But in 2016 Toyota introduced trailer anti-sway detection to the VSC (Vehicle Stability Control) adding it on all models except the SE. (Explanation below.) That is the ONLY REASON you officially can't tow with the SE.
So using the same logic one could argue you can't tow with ANY previous year RAV4s because they don't have anti-sway detection either. So do we need a campaign to remove towing hitches from all pre-2016 RAV4s? I think not!
Explanation: Trailer anti-sway control is just another of the save-you-from-yourself features that are possible with the sensors (accelerometers in this case) and computing power today's vehicles have. Pre-collision automatic braking systems are another example.
Anyone who's towed anything but the smallest trailer knows about trailer sway and its dangers. If any number of factors such as tow vehicle and trailer weight, trailer loading, tire pressures and weight distribution are not carefully considered, when a certain speed (determined by the factors above) is exceeded the trailer will start moving side-to-side on its own. Could be just a little at first, often caused by being passed by a large truck, but if either the proper counter-steering isn't done or the vehicles aren't slowed down immediately it will get more violent very quickly possible causing a crash. And yes, even with my 200,000 miles of towing experience, a moment of lost concentration had me using two lanes of an interstate to avoid crashing while trailering a friend's classic car.
Enter the software safety engineers. When a trailer starts to sway it induces a sideways force on the tow vehicle. That can be detected by the tow vehicle's accelerometers, the RAV4 in this case, and since the throttle is electronically controlled power can be reduced by the ECM to slow the car and trailer down to a non-sway speed. Using the ABS braking can also be automatically applied.
Okay, why isn't the can't-do-without trailer anti-sway control on the SE? Obviously I'm not privy to Toyota's thinking but I have a good idea why not. It turns out (again from experience) that the better a car handles the worse it will be for trailer sway control. Years ago before I bought my first travel trailer that I'd be towing with my Honda Accord (not tow rated BTW) a friend told me two things, "The good handling you love about the Honda will be a determent," and "You'll have to learn to drive all over again." He was right on both points.
The SE has a stiffer suspension and probably lower profile tires than the other models so as it goes down the road effects such as side-winds move it side-to-side less than them. Virtually any trailer will move side-to-side more than most tow vehicles so the tendency to sway is always there but will be easier to control on the "poorer" handling RAV4 models. Apparently the engineers couldn't make electronic trailer anti-sway control work to their satisfaction on the SE so rather than potentially be responsible for damages in a towing accident Toyota just said, "The SE can't tow."
