To summarise, as someone from a religious community that uses the term modest to describe clothing which looks a certain way (and part of the demographic to whom this is aimed at), I am quite comfortable with the word. I can see why some people might not like the word but it's more than a stretch to say that calling some clothing modest means that other clothes are all immodest and it's some sort of personal attack on the various posters. That's ridiculous. M&s are just saying- here are some clothes that might suit the requirements of some people.
As a Jewish women I am understandably concerned about attacks on me, on other Jewish people and on my religion. Violence and harassment against both men and women dressed in a way which shows their religion (particularly Moslem women and Jewish men) is a daily reality in the uk. And of course elsewhere. Sweeping statements about what Muslim or Jewish women do or don't do or what their religions mean from people who are outside the community and often know very little about it come across as bigotry. Unfortunately that's because most of the time that's exactly what it is.
Of course that does not mean that a religious community or a religion should not be criticised. But knowledge and sensitivity are your friend here. Rudeness, ignorance, sweeping statements and putting full stops after each word do not help persuade anyone.
No one community has a monopoly on feminism. Prejudice towards women who dress a certain way or who are members of a particular group is certainly not anything to do with feminism. Treat people as individuals and try to listen to their points of view without preconceived notions about them or that they are wrong/some sort of weak submissive women.