Thanks, I really appreciate it, and so should all Iranians !
I do not know of any hatred of Iranians towards Pakistanis. I know one Iranian woman who was married to a Pakistani man, and even though she got divorced, she praised the man as very kind and caring - I am not saying this is the rule, but this is the only case I know of, and it came out good. The hatred you are talking about might be related to politics, about the Pakistani government, and Taliban support in Afghanistan, but not directed at Pakistani people. Similarly, many people dislike the policies and government of Iran, without hating Iranians.
As for 'slaves' I never heard of it ... maybe they mean politically ?
Poor, yes, that is probably the perception about Pakistan, and there is some truth to it, but it is not a reason for hating a country, just because they are poorer. And it is all relative, Iran is poor compared to let's say UAE or Qatar, so does this make us worse people ? Of course, not.
I don't know about majority of Iranians, but seriously I have not heard bad things said about Pakistan from my Iranian friends or family, though it has not been mentioned as a topic often, but unfortunately there are many people - and not just in Iran - who think along the lines of superior-inferior. Americans think Arabs are inferior, so do the French, and so do most Iranians. Other thinks Iranians or Pakistanis are inferior. Some Pakistanis think Indians are inferior. Often there is an element of skin color attached to that, which is really an irrational generalization.
About Pakistanis, Iranians have no strong feelings pro or against, except perhaps when it comes to politics.