Moral and law is interact with each other. Law is the bottom line of moral guaranteeing its base line not to be harmed. Moral on the other hand restrict the behavior of people help law adjust the relationship between the people and society. I basically agree with the speaker that many problem in society cannot be sovled by laws or the other legal system, because of the moral cannot be legislated at all.
Before we discuss the queation, we should first figure out the unity of moral, does the moral stander is same between the different people. In my point of view, the answer is no. Moral has the tight relationship with the enviroment you live: your faith, education, traditional culture etc. We cannot deny there indeed exist the common moral, however, some moral stander is differntial from people to people. Spliting on the street is widely accepted by people as an none moral behavior because it harms the appearance of city and affect the feeling of other people. This kind of behavior can be classified into the common recognition of moral. Conversely, for the homogsexual problem, everybody may has diverse response to it. Some may think it  break the nature regulation and offense the human moral, others believe it is their own choise without any constraition can be called nature as well and do not obey the moral stander. In that case moral cannot be weighted by only one stander. But for law it must have the only one stander, no body can question its rightness, so the moral behavior cannot be legislated due to its variety.
In today's society, the majority problem is turely on the moral aspect which law and legal system is unable to constrain. Take the problem of raising old people for example, a lot of people is unwilling to care about their old parents for hectic work and pressur to cultivate their child. These ignored old man have to back to the society in order ot live a life  However there is no clause stipulate the children have to pay living expense to their parense or take care about them. What's more, some people who do not raise their old parents may unnable to afford the expense. He or her may unable to live a normal life. For the people like them, even though the moral can be legslated, it is still not a ideal solution or even aggreviate the problem lead for more confliction. However people can through strengten the ensurance system to smooth the problem, dispite the moral degree cannot be achieved for people will not be affected to take care of their parents, but the confliction is minimized. As a result,  moral legislation sometimes is not a good way to solve the problem.
On the other hand, some unity moral can be stipulated to law. Like the spliting in pubic which everyone will accepted its a bad thing. The legislation will garantee such behavior be highly valued by people and help raise the moral degree shaping the good habit for people. In singapoo due to such serious law, you never see a gum on the floor otherwise you have to pay  the higher compensation or even suffer the conviction of strip. For such problem we could try the legislation to solve the problem, but for me it is can only be called a bad solution. Moral is the thing stem from self-consciousness of people, and law on the other hand is the outside constraintion. They have intrinsic different from each other. Imagining if all the unity moral is restricted by law, we just like a robot according to the programm to behave. The legislation in only reflect the moral deficiency in a society.
In the final conclusion, the opinion of speaker is true for some situation. The moral legislation cannot be actualize, even it equip the conditoon, it may hardly solve a problem. What's more, the legislation is not a perfect solution, it is only the final method to solve the problem.