If there is something "indecent" it means that it is to be banned, that it is inacceptable. It's the meaning of the word.
The question needs to be rephrased: "Is there such a thing as "indecent dressing" in a church?"
To THAT my answer would be: No. Before God, we are all alike, no matter what we wear. Would anyone believe that God cares about the look of our clothes? If there is a God - which I do believe, but to each their own - he's seen us naked. Let people dress the way they dress. If you don't like what they wear, provide clothing as a gift. Maybe they cannot afford anything else?
Church isn't a time to try to show off some skin to look attractive. Church is a time to rectify your life with God. Dressing indecently has no place in church. Your "Sunday best" isn't "dressing skimpily." There is freedom of expression, but I doubt God cares how one dresses in church, so be good for goodness' sake.
Pastors should not ban indecent dressing in churches. When people go to church, they want to hear about Jesus. Jesus would not turn people away from his church just because they may not be dressed appropriately, so pastors need to take a cue from Jesus and deal with the dress that some people have.