On the one hand the Church has always had a missionary stance, which includes talking to those outside, and, in order to be understood, use their tongue and symbols. For example we see Saint Paul referring to the altar of the unknown deity. So in this respect – the answer to the call of Christ Himself to go and teach all the nations – a certain openness to the world, in order to communicate the Gospel, can, and perhaps even should, be exercised.
However with regard to its worship, its Liturgy: the H. Mass, the early Christians, and in fact the majority of Christianity up till the Second Vatican Council (as a point in time, not necessarily seen causally) – and certainly with respect to our eastern brothers, whether uniated or not, even up till today – have kept this holy event guarded and outside the realm of the world. Those who weren't baptised, even those who were preparing to enter the Church, had to leave before the offertory – when only the ecclesia secreta remained. When the Church became more established, even the state religion, it kept its liturgy, especially the holiest part, the Canon, set apart – by using a liturgical language, physically dividing the sanctuary from the nave (by communion rails, rood screen or iconostace), and in the Roman Liturgy the silent Canon. It is holy, and everything holy should be veiled – kept save.
I think it is a grave mistake – even an dangerous one – to use our Liturgy as a missionary tool by opening it up to the world. Of course it can be, and has been, the cause of conversion, but not by its openness but by its complete otherness – revealing our Lord by veiling. On the other hand, the modern tongue, modern music, the modern imaginary, can be used to reach out to the word, to proclaim the liberating Gospel. However not in the Mass, the H. Mass is in this respect a bridge to far!
(This doesn't necessarily say that no heart can be touched in a 'youth' Mass – since it being a Mass already sanctifies. But in this case I tend to say 'in spite of'' the 'worldliness'.)
