The bolded part is the sentiment that many are sharing and it really makes no sense. Disney could have nipped it in the bud early on but instead gave in to the earlier and earlier arrivals, resulting in the stupidly early situation we have now. This is their own private property which they can do whatever they want on. They are NOT, I repeat, NOT powerless to prevent guests from parking and lining up at the gates early. They can prevent them from even taking the exit ramp into the Studios parking lot until the designated arrival time, or they can redirect people out of the parking lot if they try to come in early. Anyone who doesn't comply can deal with the police, it's that simple. It's literally a matter of a handful of extra security CM positions.
If they did not allow a crowd to build up for two hours then there wouldn't be two hours' worth of people ready to stampede into the park, creating a situation much more unsafe than if they just opened the parking lot like normal. The process of stopping at the toll booths and being directed to a parking spot naturally creates enough of a filter to trickle people in, and giving a shorter timeframe prior to allowing guests to enter the park prevents the crowd from getting to large.
Disney is more than capable of handling the resulting crowds - see the traffic on World Drive on New Years Eve. The resulting situation wouldn't be anything even remotely close to that level of craziness and they handled that just fine because they were staffed and prepared for it.
If we want to talk about safety issues - 10,000 people lined up at the park entrance for two hours is far more unsafe than "more traffic than normal when the parking lot opens".