I am sympathetic to this line, but Scruton's dismissal seems a little facile. If somebody says the truth is relative, then they can bite the bullet if they wish and say that THAT truth is also relative, thus avoiding the trap of self-contradiction. It might still be unwise to close your ears to them.

Consider a case where we DO agree that a given subject matter is relative; e.g., taste in ice-cream. Suppose Rosie the relativist tells you: "This ice-cream vendor's vanilla is absolutely horrible, but that's just my opinion and obviously it's relative to my own tastes." You would probably agree that Rosie's opinion is indeed "just relative"... and still give the vanilla a miss this time.