legalists don't keep the law either they just pretend to. Like their religion it's just pretend.
It is just a pretense, and it's a strange phenomenon, the modern legalist. (Many are in cults, with extra-Biblical false prophets, the religion they adhere to not solely of scripture, rather scripture plus the writings of false prophets they follow.) Most of these are Gentiles, oddly seeking to be like Jews, the problem being, as you point out, they don't keep the law they claim to keep. They only honor a handful of the requirements of the law, which doesn't work in the Christian faith, as one under the law is responsible for all the law, Galatians 5:3, and guilty in one point guilty of all, James 2:10.
As to moral law, the law of love and walking in the light of Christ precludes a person from wanting to break those laws which are moral laws, Matthew 22:37-40, and these moral laws are, actually, in the hearts of mankind, Romans 2:15, societies with no Judaism or Christianity down the ages prohibiting and punishing murder, theft, etc. But this idea, if they actually do keep any law they claim, that they can, for instance, keep a sabbath or feast, or be of a certain diet and gain merit doesn't work in Judaism or Christianity, the whole law of the Old Covenant a big task, even if you exclude the sacrifices. Of course, their religion is neither found in the Bible, rather than the whole gospel is more like scraps of scripture, pasted together, with some doctrines of devils, thrown in.
None of them are keeping the law they advocate, and it's like Gentiles who seem to want to play Jew, real Jews of any orthodoxy actually knowing the law and keeping a long list. It's strange and confused, some hollow religion you see on message boards from these people, but what I most believe is that they're trolls, looking for a fight, at least those not of some cult they hide their identity belonging to.
Most ironic is that the law was only given to Israel, in the first place, no other nation. This was written by David, some reckoning three thousand years after creation:
Pslams 147
19 He sheweth his word unto Jacob, his statutes and his judgments unto Israel.
20 He hath not dealt so with any nation: and as for his judgments, they have not known them. Praise ye the LORD.
God Himself states He didn't deal with any other nation via the law, period. So, on what basis do these Gentiles think they ever needed to be Jews? Most curious, what is it they find so objectionable of the faith of the New Testament? If they're not just trolling, perhaps they can't stand the concepts of having no merit before God, this too damaging their egos, and too scary to face they aren't really in control? They also seem to completely discount the role of the Holy Spirit in a person's progressive sanctification, don't seem to believe in the power of God, rather need to have a checklist of some sort, because there's not really anything written on their hearts? They can only relate to what are simply dead letters to them, on a page, like the Pharisees? Don't really understand the gospel?
Whatever the case, here's the bottom line:
Galatians 1
6 I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel:
7 Which is not another; but there be some that trouble you, and would pervert the gospel of Christ.
8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
9 As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed.
