No, the decision was not a mistake, but you can make the right decision for the wrong reasons. It is important, because it sets precedents for future decisions.
I should have posted this in one of my previous responses, but I just read the actual article and was amazed by the terrible logic presented by the pro-law side. While I agree that there should be a moral base behind the laws, there is no evidence or reasoning that consensual sex between two homosexuals does anything to endanger families or marriage. If anything, it would strengthen both institutions, as marriage and families would be more genuine. Why? Because decriminalizing homosexual relations would reduce the number of homosexuals who feel they have to enter a heterosexual marriage in order to fit in to society. Thus, there would be fewer fake/bad marriages. The other thing that bothered me is that Scalia equates homosexual relations with rape, adultery and bigamy. Adultery (is this really an actual crime?) and bigamy have been outlawed because both are considered detrimental to families/marriage (adultery for obvious reasons; bigamy for more complicated reasons - economics perhaps). Because there doesn't see to be any reason why homosexual relations is anti-family or marriage, this is a bad analogy. And Rape is outlawed because it isn't consensual. One of America's most basic tenets is that of self-determination that doesn't encroach on the self-determination of others. Thus, it would appear homosexual relations do not encroach on anyone's ability to self-determine anything. However, the law against homosexual relations most definitely encroaches against the ability of homosexuals to determine their own lifestyles. Basically, nobody presented a single good reason for outlawing homosexual relations. I hope the lawyer was astute enough to keep this the focus of his argument.
Subtomic, I agree that the law is stupid. What I wonder is if the court should overturn a law that the legislature has passed if it isn't unconstitutional.