In a democratic system, the majority in parliament can
technically do whatever they want. But not quite, for argument's
sake. In Germany, Merkel's party won the election outright, but
because of the strong show of the other parties, she had to give
some key ministerial posts to those party, to reflect the sizeable
chunk of Germans who voted for the Opp.
You say that 'no need for debates', which is pessimistic indeed. If
the opposition is strong enough to debate critically every bill
that's introduced by the ruling party, the press would report such
debates, and therefore the pros/cons of each bill will be known to
the public, even if they are passed. Such debates will stokes the
fires of public sentiment, thereby not allowing the ruling party to
do as they wish (unless they insist on going against the prevailing
public opinion with one unpopular Bill after another, then the
ruling party will scuttle their next election).
But then again, vigorous debates in parliament is only as good as a
free press which will report on them with equal vigor. Which leads
me the the press in S'pore...