"so what is the point of having free speech then if we know it is going to be misused?"

How does one 'misuse' free speech exactly? It is what it is. There are certain limits (no inciting violence against another, etc.) but simply saying something that others find distasteful isn't misusing free speech.

"or, what is the point when western powers criticise Iran? and Ahmadinijad in particular?"

Well, I guess they criticise him because they don't care for what he has to say or for his country's behavior on various issues -- the same way that other world leaders and countries get criticised by those who don't agree with them.

"At least Nijad has not yet killed Israelis, while Israelis killed so many Palestinians kids, women, elderley and banned even medicine and normal supplies."

BTW, nice that you included the word "yet" in your post...real nice.

Israel has killed a lot of Palestinians, you're right. Personally, I don't believe it's their policy to intentionally target civilians (I know you will disagree with me on this point, because you think them murderous infidels), but as in any war, innocent civilians get killed.
I would offer that there are some Israelis who have been killed as well...far fewer, I'm sure, but they've endured casualties in this conflict as well.
Are you trying to turn this into a numbers game, who's killed more people?

Re: their banning certain materials...I can't really speak to what they're allowing across the borders into Gaza. I seriously doubt they've banned medical supplies. Other things, perhaps -- because I think the intent is to stop things that could be used to supply militants.

But back to the topic -- Western leaders walking out or choosing not to attend this conference in no way diminishes Iran's ability to have its say. You might disagree with their choice, but Ahmadinejad got to say his speech, so where is the problem?

"Most plain girls are virtuous because of the scarcity of opportunity to be otherwise."
-- Maya Angelou