The life and trials of a growing Christian - Day One Hundred Four

I got a letter and a tract today from a woman representing the Watchtower, AKA, Jehovah's Witness. I'm not sure if she randomly picked our address or if she sent it to us because we have a big cross in our yard (her return address is right up the road, so it could be either, or). I read the letter which was very nice, she even offered to help counsel anybody who had any questions.I opened the tract and immediately looked at the back where I saw the Watchtower logo. Needless to say, the tract went into the trash.
Every now and then, we will get a knock at the door and it will be some Watchtower people who are always very nice, but I tell them that I'm not interested. I also see pairs of young Mormon men riding their bikes proselytizing anyone who will listen.
Both of these groups are not biblical groups, they are cults. They have different versions of the bible and the Mormons even have extra books (The book of Mormon & The pearl of great price). The bible says in Revelation 22:18 For I testify to everyone who hears the words of the prophecy of this book: if anyone adds to these things, God will add to them the plagues that are written in this book; 19 and if anyone takes away from the words of this book of prophecy, God shall take away his part from the Book of Life, from the holy city, and from the things which are written in this book.
That sounds pretty straight forward to me; Don't add to or take away from the bible. If a group has to have their own "version" of the bible, they are lairs, no matter how nice they are and are leading themselves and anybody who joins them straight to hell!
I will give them a compliment though. They are doing something to further what they believe in. They are fearless and relentless in their desire and action to spread and grow what they believe in. They are growing, they are influencing Christians that aren't rooted deeply or who don't know any better, or who are tired of doing nothing and see the kind nature and the motivation and action of these groups.
I don't ever get a knock on the door from any of the several local churches, and sadly I don't ever do any knocking of my own. What happened to people of the church pairing up and going out and doing exactly what these cults are doing? Why do they have such dedication and motivation? I don't quite have any answers to either one of these questions but I do know that if we don't do something we're doing nothing and that just doesn't work.