Besides being against free speech, pluralism, religious freedom, women’s rights and LGBT rights, Hamas's charter also calls for Israel's destruction and they attack target civilians (which as Human Rights Watch [among others] notes, is a war crime - )
Certainly some liberals do support Hamas, with slogans like "We are all Hamas now!" and "Victory to Hamas!" ( ) being cheered. Yet, others do not support Hamas per se and would not support it without the existence of Israel and the Israeli-Palestinian conflict.
Partly it depends on what you mean by "supporting" Hamas. Certainly when it comes to a choice between Israel and Hamas most liberals would sympathise more with Hamas, and they are more critical of Israel than they are of Hamas (if they are at all critical of the latter).
In that context, liberals "support" Hamas for 5 main reasons:
1) Images of death and suffering
2) Israeli wrongs
3) Anti-US bias
1) Images of deaths and suffering
Liberals are very sensitive to other people's suffering and power relations.
In the Israeli-Palestinian conflict in general (and in 2014's Gaza conflict in particular), the bulk of the deaths and suffering are on the side of the Palestinians.
Since Hamas is on the Palestinian "side" (among other things, being the government of Gaza), liberals see the greater suffering of Palestinians as proof that Palestinians (and by extension Hamas) are the wronged party.
Hamas knows that images of Palestinian suffering are great PR and its strategy is to maximise Palestinian suffering. Bill Clinton summarises the strategy:
"Hamas can inflict terrible public relations damage on Israel by forcing it to kill Palestinian civilians to counter Hamas," he told Indian NDTV news channel.
Hamas had a "strategy designed to force Israel to kill their own (Palestinian) civilians so the rest of the world will condemn them," while Israel couldn't "look like fools" by not responding to the heavy missile attacks.
Images of death and suffering are not the only motivation, however. There is a lot more of that in Iraq and Syria, but liberals do not spend as much time and energy on the problems in those areas, instead focusing on the Israeli-Palestinian conflict.
As for power, liberals tend to support the underdog, regardless of whether it is right.
As Haruki Murakami noted when in Jerusalem ( ):
"Between a high, solid wall and an egg that breaks against it, I will always stand on the side of the egg."
Yes, no matter how right the wall may be and how wrong the egg, I will stand with the egg.
So because Hamas is clearly the underdog in the Gaza conflict, liberals reflexively support it.
2) Israeli wrongs
It is hard to conclude that Israel is totally blameless in the Israeli-Palestinian conflict.
As I note in :
the Israelis have been building settlements in the West Bank, which makes a future solution harder to achieve. Many Israelis' treatment of the Palestinians in the Occupied Territories leaves much to be desired (e.g.), and the army seems to use disproportionate force sometimes ( ). One might even blame Israel for not being more generous in giving the stateless Palestinians concessions - given that they were stateless for 2 millennia themselves.
Given that Israel is Hamas's most visible enemy in the world media (quietly, Arab leaders prefer Israel to Hamas for various reasons that I shall not go into here: ), some antipathy towards Israeli actions is translated into support for Hamas, which opposes Israel.
3) Anti-US bias
Liberals are very skeptical (to say the least) of anything Western governments (and in particular the US government) do in foreign policy ( ).
The enemy of my enemy is my friend.
In this vein, since the US supports Israel, those who are anti-Israel (like Hamas) must be the good guys.
This is similar to how many liberals supported Venezuela's Hugo Chavez despite his running the country into the ground and subverting its democracy ( ) - Chavez defied the USA, so he had to be on the side of Good.
For an example closer to Gaza, some liberals opposed the 2007 troop surge in Iraq that stabilised the country, since it represented a larger US presence in Iraq (rather than the smaller one they desired). A 2008 Gallup poll found that 79% of Democrats thought the surge either didn't help or made matters worse despite clear evidence that civilian deaths declined while military deaths did not increase (MIT economist analyzes troop surge in Iraq). Even more tellingly, in an experiment ( ), even when presented with evidence that the surge stabilised the country, many supporters of withdrawal (who we can take as a proxy for being liberal) did not change their minds.
Most liberals, especially in the West, have a background in the Judeo-Christian tradition/Western Civilization. Islam is a "minority" and so "powerless" (with reference to point 1 on suffering and power).
This is why many Liberals - even feminists - don't say much (if anything) about women's rights in the Islamic world or other human rights issues for fear of appearing "racist", ethnocentric. and/or Islamophobic. Instead they pick on trivial problems in Western world.
The Palestinians are mostly Muslim and Hamas is a Muslim organisation (as opposed to Fatah, which is secular). Meanwhile Israel is a Jewish state (which ties in to the last point about anti-Semitism), so the choice is clear.
Lastly, some support of Hamas is due to good ole anti-Semitism.
To be sure, you can criticise Israel without being anti-Semitic. Yet, when your slogans include “Death to Jews!,” “Hitler was right!,” “Gaza is the real Holocaust” and “Jew, Jew, cowardly swine, come out and fight on your own!” ( ), it is hard to conclude that anti-Semitism isn't involved.
Also, double standards abound. We hear about (and people get outraged about) Israelis cheering attacks on Gaza (presumably because they are happy action is finally being taken to stop Israelis being terrorised by rocket attacks) ( ). Yet, nary a word is said about Palestinians cheering as rockets are launched at Israel ( ).