He's a senior figure in Northern Ireland, his party gets less than 1% across the UK. Even allowing for him being a senior figure, they don't give Cameron, Clegg or Milliband columns and they haven't been in on discussions of how to kill civilians with bombs.
Northern Ireland is in the UK. Issues relating bto it are important to the UK generally.
Cameron Clegg and Milliband are incessantly in the media putting forward their ideas, policies and so on.
the association that Adams was and probably is associated with went far beyond bombs in getting their way. Whether we like it or not they have widespread support and are part of the democratic process. It isn't about liking them,