Let's suppose you like Roger Federer and think he's really great. You'd be right -- he is really great -- and it would be ignorant for anyone to say otherwise.
Rod Laver was the Federer of his day. If you'd rooted for him during his era, then you'd probably feel the same way about him that you do about Federer. And that's how those who support him in this forum feel: they like him and think he's really great. And they're right -- he is really great -- and it would be ignorant for anyone to say otherwise.
No one needs to make arguments against Laver in order to argue how great Federer is. It is indisputable how great Federer is. And no one needs to make arguments against Federer to argue how great Laver is (a point that I wish some others here would take to heart). It is indisputable how great Laver is.
Really, the two have nothing to do with each other. Sure, I'm the worst person to make this point because I just put together a GOAT list that ranked them, but the point is still true. The best approach is probably just to say that they (along with Bill Tilden and Laurie Doherty, but no one else) were the greatest of their own times and as great as anyone from any other time.