Witches

In Shakespearean times witches were blamed for everything, from falling bridges to warts. Even people's deaths from just possibly natural causes were blamed on witches just because they were that hated (or to have someone to blame). 

Why was Macbeth so topical when it was first performed?

Whenever something bad happened witches were blamed. They were evil and were known to have no sympathy for the dead, as you can see in the 2006 version of Macbeth as they were vandalizing the grave yard. 

Also, witches were known for being murderers and harming people in any way just to get a 'kick out of it '. This is why the 3 witches always mentioned death and said how the King had to be killed. 

Basically, it was so topical as everyone hated witches and to see them portrayed as this evil it would make their hatred grow stronger and have them enjoy the performance more. 

Consequences in 1605?

In 1605, a man called Guy Fawkes and his fellow conspirators planned to blow up the houses of parliament, because he didn't agree with the King and his ways. This is the same in Macbeth as it shows what it would be like if Macbeth did become the King, and with it ending up in him being murdered for being disliked.