If you feel your son or daughter must collect weapons, you should know where they are, control access, and make sure the items are legitimate collectors' pieces. Personally, I would not allow weapons in the house with children unless I was a peace officer or something of that sort. I was a collector, but before my kids got interested in guns I sold my collection. Ask about strange things, and make sure you get a solid answer before backing off. If you are successfully following the guidelines for good communications, you will probably be able to openly ask and explore with your son or daughter any unusual groups, interests or activities.
Privacy is an issue.
You get the information you must have, and then you butt out. Do not set a bad example for your kids. Stressing how you cheat the IRS or got revenge on someone should be a no-no. If there are groups or people you hate, think are inferior, or want to hurt or belittle, you are setting an example that may lead your children into trouble, and perhaps you should consider why you need to do this rather than getting on with your own life. If you scream, shout, tantrum, abuse or hit others, your children are more likely to do the same.