First of all, they are not in sin to be legalistic. The Bible itself gives us a definition of sin in 1 John. Sin is the transgression of the law. No law of God is being broken because you have church leaders imposing strict rules on the people. It is like when I have considered the Amish lifestyle or something similar. I would be freely choosing to place myself under their leadership. The Amish people are free to leave anytime they like. If they choose to remain, they need to submit to the authorities.
There is an interesting documentary at YouTube where they actually spent time with an Amish family, and even though it had a bias against them, you could see first hand how they live. It was done by the BBC. I like what I saw of how they live.
We are not under Law but under grace. Grace is the direct influence and empowerment of God's Spirit. If the Law that was given by the mouth of God Almighty to Moses is inferior to living by grace, as Paul argues, then how is it a good thing for NT Christians to now come up with their own lists of superficial laws to bind upon one another in order to walk a sanctified life? The true grace of the Holy Spirit walks in agape love and NEVER breaks a true command of God. How are Christians improving upon the Spirit walk by adding a rule book of laws loosely based upon their private interpretations of scripture? How is this not doing precisely what Paul rebuked the Galatians for, except they substitute their own rule book for that of the Jewish ceremonial laws as in Galatia? The principle is the same. Paul was abundantly clear that such, "don't taste, don't touch" rules were purely aesthetic and profited nothing in the real subduing of the fleshly nature. Buggies, hooks no buttons, bowl haircuts, and beards for married men have NOTHING whatsoever to do with following the Spirit of God, but only conforming to ideas of certain men. What you obviously fail to grasp is the danger of growing up in this system and coming to believe that the cultural system is what saves you, and let me tell you a fact that this is epidemic in these sorts of societies. I have been told this by literally hundreds of people that have grown up in that and became born-again, then suffered under the oppression of it all. Many born-anew believers are persecuted ad disciplined for having prayer and bible study meetings in these communities. Are you a proponent of the perfect law of liberty or of laws of man-made rules that take people into bondage? You cannot have it both ways, brother, and in this case I do not believe that you have enough information to determine which is going on in the real Amish community. You watched a documentary on this. My life has been intimately interwoven with this community for 15 years. Many of my closest friends grew up Amish, and I personally know Amish and interact with them every single day. In all due respect, you are looking at something from the outside without a knowledge of the inner workings of it and the spirit behind much of the control and manipulation that occurs continually, and the destruction that causes, not to mention the suppression of spritual truth in favor of traditions of men.
As far as Amish being "free to leave anytime they like", you are in extreme ignorance regarding this. Yes, they can leave....their families, often their jobs, their friends! do you know nothing about "the ban" or of "shunning"? There is virtually no freedom to live by your own convictions when it comes to the exhausting lists of rules that they adhere to. This is an all or nothing deal for them. This would not be as bad, if the name of Christ was not being attached to the whole thing. When Amish are baptized, they submit to the organization utterly, they join the Amish church, not just join themselves to Christ! They are made to take a solemn vow of obedience to the Amish church, and leaving the Amish church is breaking that vow, and there is incredible pressure applied to individuals who decide that following Christ and obeying the Holy Spirit leads them out of the Amish culture. If you agree with these tactics, then I question your grasp of scripture and its right application, and make no mistake that these are the standard practice of the Amish church, even in its milder forms. The smaller, hyper-conservative groups are brutally controlling, even cultish in radical devotion to non-scriptural cultural practices. Do you believe that one must literally kill those who leave, like radical muslims, before crossing the line of control and manipulation?