What makes you say answering amen is any more mandatory than laining?
Because I am required to answer amen to brachos. I am not required to lain.
If nobody leined, then nobody in the congregation could talk during leining. So, by your leining, you are doing lifnei iver for the whole shul.
Had I davened in a different shul, you might have a point. Fortunately, however, I happen to daven in a shul where I am the only one who talks during laining.
The Wolf