Why are so many Christians legalistic? As far as I can tell, legalism is only legalism when it involves convictions and christian liberty. Of course there are things in the Bible where there are clear distinctions, however, it seems that most cases of Christian legalism is in regards to Christians having such strong PERSONAL convictions that, in their mind, it's wrong for anyone to participate in that "sin".
A more simplistic definition that I came up with for the differences between legalism and sin:
SIN: When a person violates a clear new testament command in the Bible, OR violates his or her conscience.
LEGALISM: When a person is offended by another's actions, thinking it is sin and trying to convince the offensive Christian that they are in sin, which may have been decidely made a sin for in the life of the offended.
It also may come across as legalistic, not because the person intends to be legalistic, but they may not be sure how to express that it's their conviction.
The easiest way to make this point is by way of illustration. According to the Bible, it is very convincing that it is wrong to have babies and live together out of wedlock. Though the Bible does not specifically state this, the doctrine of separation clearly and strongly supports this conviction, there are many, many unsaved couples that choose to live together and also have children, without being married. For some Christians, that's hard to fathom and it's clear that these couples are living in sin and therefore they try to convince unbelievers of their "sin". This is a clear example of legalism because the Christian is trying to force unbelievers to do something that does not bother them nor does it make sense to them. To the unbelievers, it's cheaper and there are some real and immediate benefits. Not to mention that unbelievers do not have a relationship with Christ.
Christians act similarly towards one another, however the difference is that all parties have a relationship with Christ. There are still many cases where Christian liberty is just that.....liberty to do what you want without offending God, or self. The doctrine of separation is layed out in scripture and one principle of this doctrine is to avoid all things that may have a negative impact on your spiritual growth. There are some things that have that effect on some Christians and those same things may not have the same effect on others. For instance: watching television may be wrong to some christians because it is an obvious floodgate to laziness and complacency and therefore a sin for them. We'll call them Christian A. On the other hand, there is a young Christian family where there are 6 children, all of which are being homeschooled, and this family may see watching television as giving the mother a little bit of a break and they may even monitor how much television is allowed. Maybe only allow the kids to watch Christian animations or other harmless cartoons. We'll call them Christian B. Christian A rightly sees television in there lives as a sin for them because they are aware of the potential detriment of it. Also, of course the Bible warns of letting evil in through the eye gates and ear gates. It is also a sin because this Christian would be violating their conscious if they did watch television. For these reasons, they may be led to warn Christian B of these detriments. Christian B has completely opposite views of television and sees it as a break for the mother, and maybe the kids too, and also has no issues with letting their kids watch selected material. This is where legalism is a very clear case. Christian A feels very strongly about Christian B watching TV and tries to convince them of their "sin", but the Bible does not specifically state anything about television, and most certainly couldn't have because it was not even a thought to be invented.
The point of all this is simple. Do our personal convictions have such control over us that we need to make others abide by OUR convictions instead of trusting that they are at peace with God? Certainly, if we feel led to talk to them, as a concerned friend, we should. But to become legalistic could start to push people away and ruin the fellowship we have with that brother or sister in Christ. Convictions help us to stay in line with Christ, but our convictions......are just ours.
This reminds me of the one another verses. Receive one another as in Romans 15:7; Admonish one another as in Romans 15:14 and Colossians 3:16; Submit yourselves one to another as in Ephesians 5:21 and I Peter 5:5 and having compassion one of another and being tenderhearted as in I Peter 3:8 and Ephesians 4:32.