Public evangelism has it's place, and the First Amendment to the Constitution should protect public evangelism. As long as the proselytism does not happen on government property, or in any way in which a government could be seen as endorsing that religion, it should be maintained that public evangelism is unrestricted. Many faiths require their followers to evangelize, and sometimes in public.
We live in the information age. With everyone having an iPhone or Android, all the information we could possibly want is right there in our pockets.
If I have questions about God or the Bible, I can go look it up on Wikipedia or use yelp and find a church that's a few blocks away from my current position. I don't need someone with a sign preaching to the public and bothering me. Not only is it annoying but self righteous when someone does that. They appear as if they are here to save you as the rest of the world is so wicked and they are here to help, and if you walk away you will be damned for all eternity unless you listen to them...That sounds pretty arrogant to me.
Personally the evangelists I have seen here in the San Francisco bay area on the streets are pretty aggressive. No one needs that.
Evangelism is wrong because of how 'psychobiblical' it all is. The definition of 'psychobiblical' (See UrbanDictionary.Com) is for one to force lines of the bible on someone in just about everything that person does.
Where evangelists would stand on the street and shout at people about how they're all going to hell and how wrong they are because of the way they walk and whatnot, this is generally considered as a slamming offensive by the church. Where they may show videos and give out leaflets and posters, this is generally considered as propaganda, same as any organisation religious, political or otherwise.
If people want to go to church, let them - They DON'T need Leviticus shoved down their throats on the way to work on Monday mornings.
Restrictions on the practice of public evangelism/proselytism are not unjustifiable. When people try to convert to their belief system, it is often very awkward and weird. People do no like being approached in public places and being put on the spot about what they believe and why they believe it.