Sorry. I don't see how you can leap to the conclusion that "it is very apparent that there is something illegal going on". The man is a veteran. Meaning he is probably comfortable with firearms and is expressing his 2nd amendment rights. Marijuana is legal in Colorado. Would you have the same issue if he had beer bottle caps laying around or a keg in the garage? Cameras and covered windows. Entirely possible the he is a little paranoid or has PTSD. Unless he is doing something you can prove is illegal then his lease stands as is. Why do you feel "the tenant absolutely must go for this to be a successful deal"? I am not saying you are wrong but you haven't given a reason why this is so. If his presence is keeping you from doing something that is needed to transform the property into what you want, then go with what @Bill S. is saying. Wait out the lease and simply choose not to renew. P.S. you are going to run into a huge number of veterans in Colorado Springs and I honestly feel the issues you see from this tenant, are things you will run into from time to time in that city. Also, keep in mind that Colorado Springs is a rather smaller community and fiercely military, and very supportive of veterans. If the press gets hold of a story that spins you as anti veterans, you will have a hard time doing business there.
If any of this makes you uncomfortable, you may want to consider sticking to investing in the Boulder/Louisville area where you are far less likely to run into this type of tenant.
Best of luck with whatever you choose to do. I think it's important to comfortable with both the area you invest in and the clientele you are likely to deal with.