If your argument is that terrestrial radio broadcasts mean we don't need the laser... then why do we need the laser?

Re: interstellar invasion, perhaps not, but hard to rule out the possibility that the response we get to our broadcasts is something like a relativistic projectile.

The universe is a big place and we are a tiny planet. It's very likely we could remain unseen even in a highly active interstellar community. Announcing our presence could have consequences, or not.