There are dozens of valid uses for this beyond ad-tech. Where we use Segment it barely even touches with marketing. Most of the value for Segment is piping user lifecycle events around to every platform and service you use to help enrich customer experience. Sure, call it sales or marketing or ad-tech, but that's really just an umbrella for trying to maximize revenue-per-customer - and isn't that the point of a SAAS platform?
I think we should be cautious about throwing the terms "spyware" and "malware" around right now; there are lots of very valid cases that should be labeled as such, but if we over-use the word it just makes it harder for us to delineate between powerful tools being used for good/valid purposes or deceptive ones.