It is sometimes claimed that Catholics have no authority to defend the Faith or to teach it. This claim is false.
Those who with God’s help have welcomed Christ’s call and freely responded to it are urged on by love of Christ to proclaim the Good News everywhere in the world. This treasure, received from the apostles, has been faithfully guarded by their successors. All Christ’s faithful are called to hand it on from generation to generation, by professing the faith, by living it in fraternal sharing, and by celebrating it in liturgy and prayer. [CCC §3, emphasis added]
Catholics have not just the right but also a duty to defend the faith. That’s part of “professing the faith” and “handing it on.”
Aquinas, Etc. 
Matthew 28:19-20 commands evangelism and discipling. God has spoken and we must obey.
You’re right of course, but there are many people who erroneously suppose that Catholic ecclesiology and/or teaching prohibits lay Catholics from doing anything like that. My post presents one item of evidence in support of the facts about this.