The problem with garbage data is that it could ensnare normal users, it is difficult to identify the bot with 100% accuracy. Secondly I don't want to get into a legal gray zone, Nitter is a proxy of Twitter accounts, its a very simple front end and lightweight, but for the most part its 100% faithful to what is on the selected user's timeline is. If I start getting into the rat race of poisoning the feed I could in theory run into libel lawsuits from some demented Twitter user that thinks their reputation is being ruined because the feed is full of gore and gamer words. Third, if I start getting into the habit of "curating" the timelines I wouldn't be able to hide behind Section 203 as effectively when some cretin starts browsing child porn accounts and hashtags, most of the VPS hosting companies are aware of Nitter and when you get a nastygram from the gubmint they are more willing to play ball since you're just repacking public data, if Nitter gets a reputation for being all over the place that trust is eroded. 

Sorry I just woke up but I think my thoughts on the matter are clear enough.