Even without the spam/porn, a firehose global feed is just too much meyhem to be useful. In my opinion, the best default setup is:

1. A view for just posts from your follows

2. A view for posts + replies from your follows

3. A “discover” view that shows you the most liked posts of the day, or something to that effect

TLDR: The best way for the user-facing part of the client to avoid spam is to only show posts from your follows and a leaderboard for global.