Many of the tribes monitor the use of their tags.   Improper use will get you a downvote.  Hopefully, that will help stop the spam tags.  I always use one if not two tags to indicate what my content is about.

One problem I see is that may not always agree about what tags are appropriate.  I post an Actifit report every day.  Generally, I write a short poem about my activity for the day or share a thought on a photo I took while out walking, gardening, etc.  

Actifit automatically adds the SPORT tag,  I understand the theory that they are tracking steps, but my only connection to that tag is that I actually moved my body during the day!  It is not a tag I would have chosen for my posts.