In Desperate need of advice from the mamas!

Hey ladies.. I am having some conflicts with my 4 year old boy and his "preschool". I am going to try to keep this from turning into a long drawn out rant of events and scenarios, but here's my best at discussing this frustration. I put my son in my college children center about 8 months ago.. give or take (time isn't my strong point).. I was so excited that he finally made it through the year long wait list, as I was convinced this was the golden nugget of childcare in our area. Their philosophy is that the classroom is interest lead through the children.. so they focus activities around what each individual child is interested in.. Now to me, this sounds like a great theory! Come to find out... it may not be. Now, long before ever attending this preschool, my son and I did many activities and hands on learning at home. The environment was rich with musical and artistic activities, gardening and hiking in the good weather, and lots of exploration and positive engagement. By the time he entered actual preschool he could already do all his counting, knew his ABCs and could write his name.. and his interests were endless.. so to me, this seemed like a perfect environment.. getting to the point... This interest lead facility is also where he discovered gun play with his peers (Which I was told was restricted to outside play only and not allowed indoors.. but come to find out later, not the truth of the situation)... and with their stash of mini army guys, he has developed an intense obsession with all of these things. I am not about to keep him in a bubble from all of these things, as I understand they are everywhere. But they are not the values that I hold in my home. Now, while at "school" he has no interest in any activity except playing with the soldiers and having gun play with his friends. I have had multiple discussions with his teachers about the redirection of this play, but they maintain that due to their philosophy, it cannot be stopped. The kids just get to do what they want based on their interests.. so if hed rather play with army guys instead of practice writing or painting, thats fine with them. I understand that not all of the parents of the other children discourage such things and so they cannot allow it with some children and disallow it with others. I am getting so frustrated because it is as though my efforts as a mother are just plain useless against all the other factors in our culture. I have tried to compromise over the last few months and it has just worsened the problem. I refuse to compromise any longer, as I am wondering, what has happened to my son? I am just wondering.. does any one have any idea of how to redirect this kind of play? How can I get him to re engage with more positive things? I do not know where I went wrong, and I am looking for differently focused preschools as of now.. I hope this made sense somehow.. I really need some sort of advice.. thanks mamas!