We don't yet have any idea how many of the more disgusting acts were perpetuated by actual protestors, those who have no real side but want to cause damage or plants. As has happened in many protests, there is strong evidence of involvement from both outside sources (even early protests in Minnesota showed a large number of out of state people being arrested, very few from within the community affected) and involvement of people employed by the state acting as instigators (the US particularly has shown several of these already, but it's been known in the past to happen in the UK).
Beyond that issue, It's not unreasonable to be disgusted, but that doesn't mean anything in whether or not it will enact change. Public reaction around the time has minimal effect on the long term changes or how it will be seen in the future. I mean, I haven't yet found comparable British statistics, but there is strong evidence that the majority of Americans found the '60s protests of sit-ins, Freedom Buses, and marches as hurting the cause and horrible at the time. Now we praise them (and, much like with other movements, many of the more violent acts involved are either swept aside or glorified as a handful of acts in desperation).
We don't yet have the ability to tell whether or not a particular movements actions will result in anything at the time the actions are happening or how much outside influence - state or otherwise - is involved. Sometimes peaceful protests - of which there have been many with this - work, sometimes they don't. Sometimes riots work - we have quantifiable evidence that they can enact change, sometimes they don't. Sometimes legal pressure works - Inquest is working hard in the UK to help reduce state-related deaths and violence, sometimes it doesn't. We can't yet know which makes it difficult, at least for me, to feel strongly about the actions of the protests at a whole. Certain acts, sure, but most of the horrible ones, the perpetrators and their involvements are still unknown so I can't really classify them as part of the protest. Protests are very convenient smoke screen for shitty behaviour, that doesn't mean they're part of the protest.