Why do leftists alight with the far right?

It baffles me to no end why activists who pretend to be on the left, back parties and organisations that are clearly right wing, even fascist. For example, in Canada, we have a very active left wing that aligns itself with Hamas, the Palestinian organisation that is rightly defined as a terrorist organisation by almost every democratic regime that exists. Hamas pretends to be a political party that seeks office with official candidates, but what party has its own military? The Nazi party did, the Soviet (and other eastern bloc countries) had its own army – outside the official national military.
Backing these right wing Islamic “parties” makes no sense. The programme of these parties is simply Shiria law of Islam that outlaws democracy, voting, debate, womens’ rights. How can parties like the NDP and Liberals possibly defend linking their political fortunes to Islamic fundamentalist parties that are almost identical to Afghanistan’s Taliban? The Taliban is a party of sorts, with its own army. There are several progressive organisations to support in Islamic countries that are pro-human rights, pro-union, pro-democracy, etc…why support Hamas and Taliban?
And furthermore, why support regimes that aren’t even in place legitimately? Israel is the only legitimate democracy in the middle east; fundamentalist Jewish parties sit in the same legislative chamber as a handful of Islamic parties that represent Israels minority Muslim population…non-religious parties also fill up the Knesset that are secular in nature. Where is this variety of opinions represented in any Islamic country? No where. Yet the left in Canada aligns itself with the pseudo-democracies where opposition is outlawed (or suppressed), when they call for the destruction of Israel and reject with contempt anything that attempts to defend Israel.
Israel is no angel either; their tactics in dealing with hostile neighbors are at best questionable, at worst – criminal. But I submit that Israel is reasonably justified in its actions in defending herself against a collective enemy that wants Israel scrubbed from the map.