I know it's years late, but I'll throw my 2 cents in here. I have a 2010 Fusion Hybrid with 192K miles for reference. I also tow much larger trailers regularly with larger vehicles (F-150, F-250, T300 pushback tug...)
Issue #1, not rated to tow:
This is mainly due to Ford selling plenty of other vehicles capable of towing. It wasn't worth their time to rate the car, which brings on other liabilities. There is also a minor issue with reverse, being electric-only, being unable to move too heavy of a trailer up a hill from a stop. Overall, not anything that really means you can't safely tow a trailer (within reason).
Issue #2, Warranty:
While the dealer will tell you otherwise, they cannot deny your warranty claim simply because you tow with your car. Your rights here are heavily solidified by the Magnuson-Moss Warranty Act. Essentially, the burden of proof is on Ford that towing a trailer is what caused a part to fail. Even if the transaxle itself were to fall apart while towing, they have to prove that towing is what caused it (which wouldn't be difficult in that situation). You are very much in a better position for warranty claims due to this act. Far too few people are aware of it.
Issue #3, Powertrain
The hybrid powertrain is actually better suited for towing than just a gas engine / auto transmission. There are no wear parts, no clutches, no belts, nothing to slip, which means no added heat from friction. All gears are in mesh all the time. The eCVT allows you to be in the absolute best gear ratio at any speed, and the boost from the electric motor gets you off the line much easier than a normal car. By far the most underrated thing in the Fusion/Escape is the transaxle. As an added bonus, everything that can overheat in these cars is constantly monitored by temperature sensors. The car will shut down before any damage is caused by overheating. Your main limitation here will be reverse (in extreme cases, on older vehicles), and long uphill grades where the battery will be depleted. In this case, you will just have to maintain a lower speed. The worst damage you will be doing in the end is lower MPG and negligibly decreased battery life due to drain rates.
Issue #4: Suspension
This is probably the car's biggest weak point. When you compress the rear suspension from a couple feet behind the axle, you change the alignment on both axles. This is less pronounced on the front wheels thanks to the shorter distance from the rear axle to the hitch, but is present. The rear axle, when compressed, induces slight toe-in for handling reasons (understeer, since it's a family sedan). For long trips, this causes excessive wear on the edges of the tires. The best solution here is to add air bags to the rear coils, which is not really something most people would want to do. Also, you can very quickly exceed the tire or axle weight ratings. 200lbs on the tow hitch equates to more than 200lbs at the rear axle, as you are transferring some of the weight from the front wheels. Simply put, don't put too much stuff in the trunk when you tow.
So, in my opinion, you can absolutely tow with the Fusion Hybrid, within reason. I would put a realistic limit at 2000lbs, and you also want to stay away from box trailers if you're going to be on the highway.
Here's my Fusion towing our aluminum horse trailer (about 2500lbs). Yes, I did tow it around locally for the fun of it. It handled it fantastic. And no, I don't use the car to tow this trailer aside from moving it around the yard.
