If someone is screaming at me and ending every sentence with, "you fucking moron!", there is approximately a 0% chance I'm going to take them seriously and I'm going to assume emotional outbursts will be sent in return to any responses I care to make.
How many pro-choice people do you think are persuaded by the people screaming "murderer" outside of Planned Parenthood?
People have a limited amount of time to deal with all of the issues in the world. If you can't explain your argument in a calm, rational manner, people who are on the fence will shut you out.
See what Howard Dean's screaming did to his campaign.