No it isn't.
Please don't mistake what I am about to say as defending the perfection of the left, since it really isn't, however, it is a total fallacy to suggest that the extreme left leads to facism.
The left generally refers to a system of politics where the government is removed from social policy (mostly) and heavily involved economically. In this sense it is interchangeable with the term liberal.
Facism refers to a government that is heavily involved socially (the exact opposite of the left in this area and the same as conservatism although generally more extreme) and a centrist or right leaning economy. Occasionally you get left wing economic facists such as the BNP. However, they are not the left because they still believe in nanny state ideology.
In other words, whilst the left can be similar to facism in terms of economic policy (although this is rare even then), the two political positions are always polar opposities when it comes to social laws.
A lot of the confusion in this area comes from the input of the Nazi's. Whilst they are undeniably facist, much misinformation was spread, both by Hitler and education authorities during the cold war, that they were in fact extreme leftists. Anyone who has studied the Nazi's political rallys will know that their policies changed from one polar opposite to the other depending on who they were talking to so that they could gain the support of the communists and the facists as well as the centrists. Their party name reflects such a tactic, National appealing to the right whilst Socialist appeals to the left. However, most historians and political scientists have come to the conclusion that the socialist policies were largely abandoned by the Nazi's upon attaining power leaving them marginally right of the centre in terms of economic policy.
However, if Ardent Listener or Aqualung wish to say how they feel the extreme left can lead to facism then I would be happy to argue the point.