In a democracy, the majority decide what actions will affect the well being of society.
For example, murder, rape, theft, etc. are all unacceptable. A proposal that everyone has to wear black socks, on the other hand, is unlikely to gain support.
Abortion is an intensely private affair, and, apart from her partner, it only affects the person involved. Whether or not she has a child is no business of society.
Some religions decry abortion, and in a democracy everyone is entitled to hold their own religious views. They also have the right to try to convert others to their point of view, but not to force these views upon others.
Federal Liberal party leader Justin Trudeau, therefore, is quite correct to argue that MPs should not use their positions to try to prevent abortions, even if they have strong anti-abortion views. To do so is undemocratic.