There is danger in assuming too much. For instance, does everyone in your church know how to give the gospel? Is it possible that someone could be genuinely a believer but not know how to clearly make a gospel presentation? Could everyone in your church effectively witness to an unbeliever?
You may think that is true, but how do you know? Unless you have heard everyone make an evangelistic presentation, you are just assuming they can. Unless you have trained people to witness, you should assume that they can’t.
This is really simplistic… but it would be a pity if a believer had an opportunity to witness, and didn’t do it simply because they don’t know what to say. This is a clarion call for every church to make sure every member is trained to evangelize.