Luke 20:46 and Matthew 23:5 warns us about people wearing religious clothes just to show off. Yet, some groups claim a need to wear special clothing because they can't be like the rest of the world. Are they okay as long as they don't do it to show off as the Pharisees were doing?
There are many people who are known for wearing distinctive clothing and many reasons for dressing differently from others. Clothing is one of the things that allow people to make a statement about who they are. Some wear traditional clothing, so that you will know where they are from. Some wear very fine clothing because they want you to know that they are rich or successful. Others wear clothing to let you know that they are serious or maybe not serious. Some wear clothing so that others will notice them. It is very unlikely that Jesus was concerned about the fashion styles of his time and his comments should be taken as being directed at people who are wearing clothes to make a religious statement.
Sometimes it is a whole religious group, where everyone wears a style of clothing that is no longer in fashion. Sometimes it is only the leaders of the group who are expected to dress differently (like robes, vestments or reversed collars).
The reason usually given to justify wearing distinctive clothing for everyone in the group is because Peter said that Christians were to be a peculiar people (I Peter 2:9 KJV only). "Peculiar" can mean "special", which is how all the other translations translate it. However, it can also mean "distinctive," and I think they are going for some form of that. Therefore, they see it as similar to a uniform - something worn that makes them stand out from others, so that others will know that they are Christians.
In Luke 20:46 Jesus warns about not imitating the scribes who loved to wear long robes among other issues. There is nothing inherently wrong with wearing robes or even long robes. What made it wrong was the reason they were wearing the robes – they wanted to stand out because the robes were a symbol of their office.
In Matthew 23:5 Jesus condemns the Pharisees because they made the trimmings on their garments bigger than most people did. Most of the articles of clothing that Jesus described were actually required of all Jews (Numbers 15:37-40). Somehow, though, the Pharisees managed to corrupt, through the use of size, what was supposed to be a command of God into something that made everyone take notice of them above all the others. Jesus was condemning those who were trying to use their clothing to make a statement about their piety. "I'm extra special, and I need to indicate that by making sure I stand out."
There is no difference in how the Pharisees are wrong for wearing clothes to impress their friends and anyone else doing the same in our age. Jesus did not just condemn the Pharisees for just showing off to other Pharisees; they were trying to impress all the Jews. And there really isn't anything in the passage to say that it was limited to the Jews. For all I can tell, they may have been trying to impress the Samaritans and the Romans as well.
Jesus was saying that their attitude was self-centered. They happened to use clothing to express that attitude. In our day, we have a lot of people who do the same thing when the priest or pastor wears distinctive clothing (from ornate to drab) to make sure that they are identifiable as clergy. Some have their choir wear robes. And of course, some are known for wearing clothing from different by-gone eras. I certainly can't speak to all of them, but if they are not doing exactly what Jesus condemned, then at the very least they are flirting with it.