Good-Old Open Door-in-Your-Face [Video]
While in some states and countries lane-splitting at low speed and obeying several other regulations is deemed legal as it was proved that it helps better the traffic, this does not involve any extra security for the rider.
There will always be silly drivers changing lanes in several feet without checking their mirrors and without signaling, and by all means, there will always be passengers who would open the doors of the cars to get out without taking any precautions.
Trucks or scooters approaching from behind, it doesn't matter for such guys. The only difference is that if they got hit by a truck, they'd be severely injured or killed, whereas opening the car door in front of a scooter or even larger motorcycle will most likely turn bad for the rider. Watch out and watch out even more when splitting lanes!