It's simple really.
1) It today's society - esp in North America - saying you "don't like" something has become equated with "hating" it. Actually "dislike" and "hate have become interchangeable, even though they mean pretty different things.
2) Everyone loves to look down on something or someone, or simply to complain about some product because its popular to do so - therefore "hating Touchwiz" has become cool to do, similar to how some people "hate Apple".
Is TouchWiz perfect? Nope - nothing is. Does it suit some people's needs? Sure - look at the success of the Galaxy lineup. They've sold millions and millions of the things and they all have TouchWiz. However, a vast majority of users don't know that they can change launchers and (almost) eliminate the "ugly look" it has. The most vocal ones who complain are ones like you and me who browse forums as part of daily (or weekly) routine. Most people just use it and don't think twice about it. They either don't know (or don't care) about the options to change it or whatever.
Do I LIKE TouchWiz? I think it's a little to in-your-face visually, and I think they could really re-write the code to make it more efficient (and eliminate some of the "features" they keep throwing in). But that's just opinion - its not enough to keep me from buying a Samsung device. I'll buy a device as a whole based on how it fits my needs/wants. Not just ignore a great phone because everyone else thinks I should - based on software.
At the end of the day, there's only one person who has to use the phone on a day-to-day basis. You. If YOU like TouchWiz, great - keep using it. If not - great, change it up. (Replace the launcher, or buy a device from a different manufacturer, or root and ROM it, or...). Who cares what someone else's opinion is of what you find works for you? If it works, good. If it doesn't, find a solution. All that matters is that the device meets YOUR needs - not the opinion of some person hiding behind a screen-name and a keyboard.