How did that controversy become so explosive? Well, one way was anti-open theists misrepresenting open theism to non-theologians, pastors and lay people, as, for example, belief that “God gives bad advice” and belief in an “ignorant God.” Many of them went directly to denominational conventions and got resolutions passed against open theism by frightening delegates by implying that open theism is a Trojan horse for process theology. (They would sometimes spend more time talking about process theology than open theism and allow the scared delegates to think they are basically the same.)
I’ve often wondered why open theism, of all things, led to such hysteria (and sometimes outright dishonesty) among its critics. One thing I suspect is that many Calvinists realized that if many evangelicals adopted open theism, one of their strongest arguments against Arminianism would be nullified—that Arminianism cannot explain how God foreknows future free decisions of creatures without in any way determining them.