I am a trade unionist. One thing people assume when you talk to them about unions is that unions and socialism are synonymous. They wouldn’t want to be part of a union because unions, according to them, are anti-establishment. LOL. This is farrrr from the truth. Unions are not inherently socialist. If anything, unions are essentially reformist entities, seeking progress and fair treatment within a capitalist society, not against it.
This does not mean that union work is futile. But union work is not calling for socialism, but rather improving the current capitalist system.
Are there socialists in unions? Yes. But not everyone is.
Why are you part of a union then? Well, first, I am part of a union because I have to perform in this capitalist society. When there are only two choices in life, work my arse off or be homeless, I'd pick the former. But I do not want to be a slave to the system. Being part of a union can significantly heighten worker's awareness of the broader socio-economic dynamics at play in a capitalist system.