Masses with or without Christian rock music are equally susceptible to irreverence and practices that are contrary to liturgical norms described in the GIRM.
IMO, it is absurd to believe that any style of music is inherently irreverent. Psalms in particular mentions all sorts of instruments known and lost in praising God.
Many “traditional songs” are inappropriate during certain church seasons, and it is just as possible that certain contemporary songs are inappropriate as well.
The biggest potential for problems at Life Teen Masses, IMO, is a music director that is too showy. On the other hand, our choir director has the same problem at adult Masses.
I guess it is customary to raise your hands in worship at certain parts of the Life Teen Mass. I have often envied the guitar players, because I am just not moved to do so. I simply keep my hands folded in prayer, fingers uncrossed (I just like that, and I know this is shallow, because it looks more angelic, and also because it takes a degree of self-discipline to do so). People should not be made to feel uncomfortable worshipping as they feel called, within reason and within the recommendations of the GIRM, of course. I’m talking about things like raising arms and holding hands, not kneeling vs standing on your head.
Life Teen has brought many young people to a greater understanding of their Catholic faith. So have many other legitimate movements within the Church that others find distasteful.
My fiance comes from a great Life Teen parish. I come from a progressive

but musically traditional parish (not ultra-traditional, just typical Breaking Bread books). We will incorporate both styles at the wedding, but leave out the drums and the electric guitars to avoid giving anyone a heart attack. My dear old Dad, a great guitar player, didn’t feel particularly called to the adult music ministry, and is now doing music at Life Teen at their new parish. Mom, very traditional, has commented to me how beautiful some of the songs are. Sometimes I think people have contempt or discomfort due to contemporary Christian music simply because it is unfamiliar, and they can’t participate fully in that aspect of the Mass. This was the case for me when I first started attending Mass at my fiance’s parish. It is my genuine hope that every person would come to appreciate, respect, and even enjoy all forms of music when performed to the glory of God.