I don't think its any worse than any other network to be honest..
The problem is its too easy to get an SMS gateway to flood over a 1 million numbers (via a CSV upload and a copy of the National Dialing Plan via OfCom) at a time at pence per message and the pay back is huge, if only 2% do something stupid..
The problem is, as it is with email, is some people send legitimate messages out that look exactly like spam, so it needs independent heuristics and scanning software to detect in volume spam, and Threat Actors.
In my view
This is not customer services and we dont have access to your account
I do not work for o2 or any VMo2 /Telefonica/Liberty Global Company
