The question is whether or not it's actually favorable to employees and whether or not Walmart will inform them of the costs they'll be responsible for. "Here's $10 to deliver this" sounds great until you realize it's $5 in gas, your insurance is going up $50 a month, and your car will wear out a year faster.
People who make ten bucks an hour are really sensitive to these kinds of costs. If Walmart institutes a program that isn't worth it for employees everybody's going to know within a week.
"Hey, there's $10 in it for you if you drop off a package on your way home." Let the employee decide if it's worth it or not. So long as there is no coercion, I don't need Walmart to educate the employees on maintenance, the cost of gas, etc. I do think it's fair and reasonable to disclose/inform/explain the insurance situation.
That's like saying criminal defendants shouldn't have lawyers because they aren't "idiots".
The problem is that the negotiation between the corporation and the worker is skewed by information asymmetry. Furthermore, the cost of changing jobs is high, and the same negotiation disparities exist elsewhere.
Collective bargaining would address those concerns, as it allows workers to amortize the cost of analysis across all their transactions. But labor unions are a heavyweight solution.
It would be nice to see other suggestions from people who don't wave off concerns over information asymmetry as paternalism.
One alternative to this program would be to buy each store a Fedex style van (or a few) and have a few dedicated drivers make deliveries all day. Once you think about that for a few minutes, you start to see all of the costs that they're offloading to employees. Not just insurance, but also vehicle maintenance, gas, etc.
I'm sure Walmart has done a ton of cost/benefit analysis and churned through a lot of data before deciding to offer a program like this, and the employees will almost certainly not get all the details.