Bottom line, parliaments are better because they have more parties represented... If you're a Republic like the one we live in, there's too much pandering. Our forefathers we're scared of this very thing and we're trying to avoid it
I fail to see how the constitutional differences between the US and the UK affect the number and behavior of political parties. My understanding is that the UK has more than two parties, but that these additional parties are very weak. In the US, divergent political views coalescedinto two parties, and divergent viewpoints within those parties tend to not leave. Vote-splitting tends to weaken minority views. Political equilibrium also tends to create a two party state of affiars. Different factions tend to stay withing the existing (big) parties to retain a voice. Incidentally, in the US we have other parties, they just don't wield much power. Even the Republican party was once a third party, formed out of those politicians opposed to slavery, Lincoln of course being it's first President.
Even with many parties, pandering can and does exist. Pandering is the result of democratic politics, and not in these cases the particular structure of the government. Also, with too many parties, it becomes more difficult to form a governing coalition. Such a deliberative body may find itself too fragmented to govern effectively. This is what happened int he Weimar Republic before Hitler and Spain before the civil war.
Of course, as one who finds it difficult to resist the pull of Anarchist political and economic philosophy, an impotent government is a very appealing idea.
BTS