In reply to J1234:
A trade union is a collective of individuals joining together democratically to address the situation where the employer has a monopoly on power and can impose oppressive conditions on workers.
A democracy is also a system whereby power is held collectively and democratically, to address the situation where small groups of people have a monopoly on power and can impose oppressive conditions on the population.
Based on these first principles there shouldn't be any question, union funding couldn't undermine democracy it could only extend it.
The issue comes when not enough people understand or care about how democracy works and the levers of power become captured by the small unrepresentative groups again. This can and has happened in any setting including within trade unions, within the Labour Party, and within our wider democracy.
Your point about having a huge war chest if lots of individual members chip in is exactly how has been for the last 5 years.
https://www.google.com/amp/s/amp.theguardian.com/politics/2018/aug/22/labou...
Healthy for democracy which is why it's sad to see Labour begging for corporate paymasters now.