“Silenced” here means any manner of active suppression (shaming, ridiculing, verbal abuse, social bullying, even physical violence, etc) of an idea, rather than simply (1) ignoring it on a personal level, or (2) responding to it with argument via evidence and reason.

If an idea we disagree with is rare or harmless, we often ignore it. If an idea we disagree with is more common and worth refuting, we should respond to it with debate. If all parties involved in a debate are reasonable, consensus is possible. In aggregate, humans are capable of being reasonable, thus society progresses over time (amortized).

Sadly, there is often difficulty reaching consensus immediately — especially with deeply entrenched viewpoints. However, given time, history has proven over and over that truth prevails though patient use of rational argument. It is only through presentation of evidence and calm, rational argument that society progresses.

Other, more heavy-handed means of ideological conquest have more often than not made the world a much worse place. In fact, more than just a few million deaths have resulted from what we could call “non-rational ideological conquest” (which inevitably manifests in progressively more violent ways).