Definitely. I do A-level maths and it's great; because every single person in the class wants to be there and wants to learn (either just because they like maths or because they need maths A-level to get into their course). If maths A-level became compulsory, I think that those who actually want to do maths won't get the grades that they need or deserve simply because of the distraction of the people who don't want to be there.
Plus, for those made to do maths, it'll take away from the time they spend on the subjects that they actually did want to do and then those grades might suffer.
I don't see anyway to win by making maths compulsory at A-level.