You need someone on your side if allegations are made against you. You need protection if your job is one that is at risk of redundancy as education budgets are cut even further. You need protection if you are expected to take on responsibilities which you are not recompensed/trained/signed up to when you accepted the position. Most teachers wouldn’t dream of setting foot in a classroom without union membership. An LSA will be in just as risky a position.
Yes, definitely. Working with teenagers has always been risky in the sense that it is unpredictable and ever changing but that's nothing to the way schools are managed these days. You need to be protected against redundancy, questionable contracts and have the opportunity to query your terms and conditions of employment (which are now subject to change at the whim of school leadership) with appropriate support.
Teaching is one of the most unionised professions in the country, with good reason. The NUT and ATL amalgamated last year and now represent people across the whole education profession. Here's a link to their site, you can join for £10 at the moment: neu.org.uk/join
Yes. I've taught for donkey's years. Do not set foot in a classroom without being in a union. I love my students - but I've had pupils blatantly say to my face, 'I'm gonna get you done' in many schools I've worked in. I have luckily only needed my union once - for a ridiculous accusation (6ft 4" 16 yo boy claimed I had 'assaulted' him in front of his whole class - and reported me to Head. I was 7 months pregnant at the time. And fortunately entire class backed me, but it was not pleasant. We still needed to demonstrate that his allegation was being investigated and I had a union rep with me at every point).