Let's say A had some theories, and said what they are, and went out and killed some people based on those theories. And let's say that B had some similar theories, and said what they are.
Rejecting A's ideas because those ideas led A to murder is somewhat defensible. It's evidence that there is something deeply morally flawed in A's thinking.
Rejecting B's ideas because they are similar to A's is shakier. B's ideas deserve a hearing on the merits. (Ideas have consequences, and A has shown what A thinks the consequences are. Those consequences can reasonably be considered part of the "merits" of A's ideas.)
Rejecting A's ideas because those ideas led A to murder is somewhat defensible. It's evidence that there is something deeply morally flawed in A's thinking.
Rejecting B's ideas because they are similar to A's is shakier. B's ideas deserve a hearing on the merits. (Ideas have consequences, and A has shown what A thinks the consequences are. Those consequences can reasonably be considered part of the "merits" of A's ideas.)