Weak words

There are words that are weak. They make statements weak. Consider the following statement:

Walter Payton was the best running back to ever play the game of football.

The statement above is an opinion that can be backed by strong arguments. The reason that the statement is strong is it is a simple specific statement with a specific subject and a simple direct object.
In a small cadre of competitors: Barry Sanders, Jim Brown, Emmit Smith; there are few who can challenge Payton for that title.
Whether truthful or not, the statement carries some weight. If I were to say that to a die hard Cowboys fan they would likely say words to qualify or correct my statement, or to weaken it.
One way we could weaken the statement is to remove the superlativity of it.

Walter Payton was one of the best running backs to ever play the game of football.

Nobody could argue that Payton wasn't one of the best running backs in the history of the game. The statement is still fairly strong, but I be I could weaken it a bit more.

Walter Payton was arguably one of the best running backs to ever play the game of football.

Walter Payton was perhaps one of the best running backs to ever play the game of football.

The words arguably or perhaps water down whatever statement they modify. Each of those modifiers erodes the substance of the statement. Why not go completely overboard and say something like this:

Walter Payton perhaps could possibly be considered one of the better running backs to ever play the game of football for the Chicago Bears during the 1970s and 1980s.

The above is an exaggeration, but I hope it illustrates what adding weak words to a statement can do. People add these words to their statements because they think they can say something without having to back it up. If you put perhaps, arguably, or possibly, you can really follow it with any statement.

The moon is arguably made out of white cheese.

It can be argued, but it isn't true.

The SEC is perhaps the conference that complies the best to NCAA regulations.

If by perhaps you mean isn't, then yes.

Of the active quarterbacks in the NFL, Rex Grossman is possibly one of the best.

If your criteria for better is the lowest QB Rating, then possibly yes.
As you can see, adding vague qualifiers to statements takes the value out of them. You can really say anything. You can say anything because what you're saying doesn't have any meaning.
There is a word for words that have no meaning, noise.