The president's diplomatic outreach to a regime founded on religious laws that systematically oppress its subjects and prohibit free speech should ring a very sour note in the ears of anyone who lays claim to the label "Liberal." Liberalism is about liberty, freedom from oppression by powers beyond the individuals' control. While reasonable people may disagree about the scope of that principle, its beyond all doubt that jailing bloggers is not a liberal thing for a nation to do. Extending the olive branch to such a nation is not an exercise of liberal principle, its a ugly manifestation of realpolitik.
I therefore encourage people who do espouse the principles of liberty to view Obama's outreach to the Islamic Republic of Iran as a betrayal of those liberal principles. Expressing support for the oppressed people of Iran would be a liberal thing to do; expressing support for the religious elite that exercises the oppression is nothing more than an attempt to get them to be nice to us and hopefully stop trying to arm themselves with nuclear weapons.
On that last point: non-proliferation is a very worthy and important goal, and it could be argued that for the world's sake, it is better to ignore the human rights violations of Iran in order to not antagonize them into an arms race. But again, that's not liberalism, that's realpolitik. If you ascribe to the realpolitik view, at least have the chutzpa to come out and say it rather than hiding behind the veil of liberalism.