I'm not sure why anyone would be against Antifa and particularly BLM though. I mean BLM have actually come out and said they don't support these protests. Read their national statement. They don't support the protests, they have condemned the violence and at no point had called for the tarnishing of war memorials. The problem is we have a media, egged on by lots of right wing outliers who get given prominent platforms who are allowed to share misinformation that makes it look as if BLM are doing this stuff. It's patently untrue. They are a community based organisation, that believe in none violent protest and trying to help and support the black community.
I think for a lot of people who have it clear they are against them, there is probably some ignorance about what they stand for, which is forgiveable. I don't think thats racist, it's just people have not taken the time to read their statements and unfortunately take what a hostile media say at face value. I have to say though, the prominent political figures, who are leading movements against them (Your Tommy Robinsons, Katie Hopkins, DFLA etc) who do read such statements, it's hard to come to any conclusion other than that they are racist if they believe a peaceful organisation who want to help their own community are wrong and need to be opposed.
As for Antifa, in essence we are all antifa as it is short for anti-fascist. There's a section I don't really agree with myself. I don't like the fetishising of violence and have never felt it is a particularly useful tactic against fascism.
In both instances though, I do think it's worthwhile acknowledging what the organisations stand for, at the top of their organisations, and what people do on the ground are different things. Thats my two pennies worth anyway.