I get so tired of hearing this argument from people. Unfortunately, so many uninformed people perpetuate this myth that it is accepted as fact and posted here by people who think they 'know'.
First, read the research. To keep it simple, there are fast twitch, slow twitch, and in between fibers. The in between can be recruited for the activity they are trained for, but will never be fully fast or slow twitch fibers. The idea/belief that endurance running does not work the fast twitch fibers and that as a result you lose them is like saying if I did not use my thumb for a couple of months it will fall off. Likewise, we don't lose explosiveness or agility because of running. Because I am a distance athlete, I can never be explosive or agile? I have lost that ability FOREVER? How does that even make rational sense?
Second, how many xc programs are just running miles? As has been said by several here, many aspects of xc involve development of fast twitch fibers. The research even says that endurance running involves fast twitch fibers and that sprinting involves slow twitch fibers. Nothing works in isolation. Case in point- look at Michael Johnson's training in college. There are distance days and hill days. Also- Maurice Greene ran early season college cross country races while he was in junior college. By the rational posted here, those guys could have run much faster had they never done that. Really??
Third, what exactly is it that soccer players/practices do that develop explosiveness? Dozens of our athletes go on to play soccer in college at a variety of levels and I have observed their summer training. The most explosive it gets is shuttle runs and sprints- apparently those are a staple of college soccer programs. That develops explosiveness? That is making them a better athlete and keeping them from falling into the perils of the endurance athlete? No way......
Fourth- and I think most important- is this: there is a time and a place for everything in a training program. I think most soccer coaches do not understand a year long training cycle, which is unfortunate for a sport that relies upon endurance. A soccer kid is not going to be hurt by running xc. They aren't stepping off the xc course and going right to their first game. Any idiot can see that some endurance training should be part of a soccer training program. The xc season can serve as a nice base/launch into more soccer specific training while maintaining the endurance gains made during xc season (which in my experience, very few soccer coaches do). The endurance gained from xc will help that soccer athlete better train to be explosive and agile because they will be stronger. I have a friend that played professional soccer and 5 - 8 mile runs were a regular in their training program.
My suggestion is always this- if a kid wants to run, he should be able to run. If they are worried about year round training that involves fast twitch/explosive/agile movements, then they should be in a strength program that targets those things- which will help make a better total athlete anyway. It is the lack of that that hurts the athlete, not distance running.