Short answer: The looters are looting, the vandals are vandalising, the protesters are protesting. They are not one and the same, and peaceful protesters are a BIG majority. You can support Black Lives Matter even if you disagree with some of the things being done by other supporters.
Longer answer: Did you ever vote for a political party but not agree with all of their politicians’ words, actions or even just personality? Would you support a friend through a bad break up but disagree with their actions when they cut up all their ex’s clothes?
It is of course possible to support a movement whilst also condemning the actions of a handful of other supporters, since they don’t represent the masses or the main cause.
I (Kãmil) do it ALL of the time. Because I (vocally) disagree with looting. I (vocally) disagree with rioting. I (vocally) disagree with hurting police officers and animals. But I 100% (vocally) support a movement for equality. It baffles me that anyone can’t or won’t support a movement for equality whilst using the actions of a minority as an excuse, when actually the quicker everyone (vocally, non-violently) supports it, the quicker we’ll get to a peaceful solution.
I also think it’s important to try to understand why people are resorting to looting or violence, and no, understanding is not the same as justifying.
Here is a longer video explaining why Amy Cooper, George Floyd and systemic racism has driven people to this overflow of anger and frustration.
And here is a thread with reactions to these acts. You’ll see you’re not alone in feeling that these are not the way to gain support, but again, I personally think it’s a poor excuse, since it's very much possible do both.