What is the point of identifying offensive tweets? People who want to post the tweet will do it anyway.
An ideal may be a customized algorithm per user. What offends me may not offend you. Of course, a trade off of that would be a growing filter-bubble...
Another way to be offended though is just for jerks to say horrible things to you. Maybe that could be beneficial in terms of developing tougher skin or something, but it seems like that should at least be an optional thing. You might get tougher skin if I rubbed you with sandpaper for twenty minutes a day - but I should probably get your permission first.
Not disagreeing with your main point but in my experience it is usually the opposite, people with “cosmopolitan” views being offended by “cloistered” takes, but eventually growing as individuals and coming to understand why they think what they do