I'll tell you a short story. My colleague was asked to make a website with a forum for part of the company we work at. I made a list things he needed to do in order not to have too many problems. One thing was using a decent captcha at the login, he ran out of time and didn't use one. After 1 month in the forum section there were 17,000 fake accounts posting stuff about v14gr4, russian women eager to meet the love of their lives, ink cartridges, ray bans, rolex watches and so on. That's 17,000 accounts, not posts, I was too scared to find out how many actual posts there were. Had to tell him to delete the forum before it was even launched if there wasn't time to do it properly. That's why captchas exist. It's like the wild west on speed out there on the internetP.S. I don't like them either.
I do not dispute the Captcha.
I dispute the fact that they are very poorly conceived and most of the time requires several tests before validating your entry.