Unions can have...problems, but fundamentally they are just people banding together to leverage the only capital they have. They can be frustrating (much of my family is in mining and mineral extraction on the ownership side so unions are a long standing fact of life in that sector) but the idea is not, at its heart, terrible.
Government regulation is necessary as a counterbalance to the vast power of the market (and market players). The market, even when left alone, is subject to distortions and issues -- some of which cannot be fixed from within that same system. There needs to be checks and balances between the market and government, but each needs the other IMO. Ideally, the government has a light touch and represents encoded hard earned wisdom protecting the public from things like hard to trace externalities etc. and fending off nasty things like monopoly and acting as a hierarchical repository for information the public may need. Of course, it takes constant vigilance to maintain a balance, but that is life.
I think each of us gets far more value from our taxes than what we pay, for the most part. I'm sure it could be better but, with all human built systems, some inefficiency should not be a surprise.
I don't know if I agree with all of Sanders' policies, but I am a bit of a demand side person. Helping alleviate some of the egregious distortions of the market we've allowed to come about and accept as normal, especially on the lower end of our socioeconomic spectrum, would likely create more value for everyone starting from the demand side, so, overall I support his candidacy.