No, for two reasons. First, a company always has far greater negotiating power than an individual worker. Second, the company's incentive is to spend as little money on workers as they can get away with, in order to maximize profits. As a result non-union jobs almost always pay less and offer fewer benefits than unionized jobs.
So even if a company could be convinced that they should not ask warehouse workers to pee in a bottle instead of taking the time to go to the bathroom, workers still come out on the losing end when they do not have a union.
"You could just as well say you are giving yourself up to the whims of the union leadership"
Workers have a say in union leadership decisions -- at a minimum they elect their leaders, but in most cases there are other ways for people to be involved. So unless the workforce also represents a significant fraction of ownership of the company (very unlikely for any company of significant size) they will have far less say in management decisions than in union decisions.
"People shouldn't have to join a particular union"
That is standard union-busting propaganda. It sounds great to give people a choice but the reality is that it reduces union representation and gives management an advantage over the workers by keeping them divided (among other things, it makes a strike far less effective and far less of a threat). The reason unions demand that the entire workforce be part of the union is to ensure that the union can negotiate with the company on equal footing -- two big parties negotiating, not one big party dealing with many small parties.