Whenever someone thinks that we’re binding something that we shouldn’t be binding (like singing a cappella in worship, or limiting the public leadership role of women in the church), that’s when the assaults of legalism are hurled at us. This, of course, is meant as a sharp 
criticism and is intended to get us to back down and/or minimize our influence upon others.
One dictionary defines legalism as “strict, legal adherence to the law or to a particular code, as of religion or morality.” In the realm of religion, another dictionary has, “the judging of conduct in terms of adherence to precise laws.” Hmm! Sounds a little bit like these statements: “Why do you call Me ‘Lord, Lord,’ and do not do the things which I say?” (Luke 6:46). “Keep my commandments…do whatever I command you” (John 14:15; 15:14). “The dead were judged according to their works, by the things which were written in the books” (Rev. 20:12).
God has a law to which He expects every person to adhere! Call it by whatever name you want, but seeking to closely and strictly follow His law is not a bad thing! It’s an eternal thing!