It depends on the law. I had anal sex before it was 'legal' in my area, and that didn't seem like it was hurting anyone else. I went topless before a law was passed making it legal for women in public areas. I just missed the 'blacks can't use white bathrooms/drinking fountains/education system' laws, by a few years. Abortion never really became 'legal' where I live, but it's also not really against the law. Spend enough time in an NICU or a hospice and you'll see that sometime moral issues and caring for individuals might matter more than the 'law' does. If I'd been my grandparents' age in the 20s I'd probably have joined them in still consuming alcohol during the odd Prohibition era.
Laws change, often capriciously, and they're often made by people who want to be re-elected. No one could have predicted anything like the institution of the original "Patriot Act" when it was enacted in the U.S., or the ever changing 'laws' for what a 'war criminal' is in the Hague.
In general, I think that laws help society function more smoothly, especially when the judiciary is in touch with the legislators and the people and society that the laws are supposedly designed to help. That seems to be less and less likely in a lot of the world- not only issues about varying ages and legal issues about consent to sexual activity, but racial issues involved with populations that are actually charged and convicted for minor offenses, 3 strikes and you're out type legislation, the lack of regulation or any type of legal controls or goals on the internet, 'obscenity laws' varying according to where you live, the culpability of soldiers who act under orders, some nations doing whatever they want against 'world' laws because they're powerful enough, etc.
It depends on the law. If I run out and murder someone or assault them or run a red light then I expect to be charged with an offense against the law. That's a moral decision for me, but also a legal one. You can't have vehicular traffic or a lot of people living in a heavily populated area without some laws.
But I don't assume that legislators are the best arbiters of what should and shouldn't be legal. There are still some parts of the U.S. that don't think that same sex marriage should be 'legal', or be given a chance to vote, or who believe that everyone should have seemingly unfettered access to a lot of weapons, or be forced to carry a pregnancy to term if they don't want to- sometimes legal issues lag well behind moral issues.