Why it is unfair to compare players from different eras..

Michael Jordon or LeBron James, Pete Sampras or Roger Federer, Pele or Maradona, Maradona or Messi? Such debates have been making fans scratch each their heads to prove a certain sportsman. Such situations where players from different eras are compared, it's very difficult if not impossible to draw any conclusion due to many factors. In basketball, it might be the hardcore playing style in earlier days compared to the ultimate professionalism that has come in the last decade. In football, it's the playing conditions and facilities that can deny any argument. There are 'n' number of factors that come into consideration. So to go on and say that a particular player is the greatest ever makes very little sense to me.
     It applies for cricket as well, doesn't it? What are the famous debates in cricket? Let's try and understand with a couple of examples. The best non Indian example is without a doubt The 'Lara vs Richards' argument. This is a debate they have in every bar in the Caribbean over a few rum and cokes. At the end of it all, everyone find themselves sitting on the fence. The older generation talks greatly about Sir Vivian Richards and his swagger. It is true though as they say he was all about - 'I am Vivian Richards, you can not bowl at me!' Things he did at his time were unprecedented and unimaginable. If Richards faced some of the greatest bowlers and still achieved tremendous success as a batsman, Lara scored 400 in a test match and 500 in a first class match which was unthinkable in his time. They say Richards is the most destructive batsman to have ever played the game but I don't think many could argue with the fact that if you wanted someone to chase 400 on the last day of a test match, on most days you would go for Brian Charles Lara. Though Lara vs Richards is a great one, 'Tendulkar vs Kohli' is elevated to another level. When Tendulkar retired, everybody thought that his records will never be run close by anyone. Especially the ridiculous record of 100 international centuries was considered to be next to impossible but Virat Kohli is making it look seemingly possible. Virat himself says that there is not point in comparing him with a person because of whom he picked up the cricket bat in the first place but comparisons are ought to be made and the perception is that Sachin is greater in tests but nobody can argue with the fact that Virat Kohli close to being the greatest limited overs batsman of all time. They say Sachin faced tougher bowling line ups than Virat and there was no power play for the best part of his career and Virat is playing in 'batsman's era'. But at the end of it all, you have to play who you get to play. Former Liverpool great Steve Nicol once said - 'You can only be as good as you are at the time, whether it be 50s, 60s, 70s or 80s!' and it's hard to diagree with it. Therefore to go on and say that someone is not good enough to be greater than someone you prefer is not right. But more importantly, it is unfair to take away the credibility from a player of one era in order to make an argument for a player from another era. For example, even if we consider that Virat is playing in batting friendly era, he has an average of 60 when all his contemporaries are below 50! Therefore instead of comparing numbers and records, we have videos of all these people, we can see how they move, how they play, how they bat, bowl and field in case of cricket, how people defend against them or don't defend against them in case of football. We can judge their attitude and dedication towards their respective sport but to judge anyone just based on numbers just makes no sense to me no matter how good or bad those numbers be!