I agree with you about the state being given a free pass on violence and coercion, as well as some corporations having done the same. What you failed to mention is that unions have abused many of their members, used violence against replacement workers, and destroyed the property of their employers.
This is not an issue of unions vs. corporations vs. states; it is the fundamental problem with collectivism, which frequently uses coercion as a means to achieve power or theft.
I agree with you, except for one part. I'd correct your closing sentence to
"It is a fundamental problem with humanity, which frequently uses coercion as a means to achieve power."
Collectivism is a slippery concept and seems to amount to "individuals working together to achieve some aim." So long as you have systems of interacting individuals, organizations will arise to achieve economies of scale, and violence will inherently be part of it because of the components that make up the system.
Based on your definition of collectivism, I would agree with you, but I think the definition is too broad.
From the Wikipedia article on Collectivism:
"Collectivist orientations stress the importance of cohesion within social groups... and in some cases, the priority of group goals over individual goals"
You can have individualists "working together to achieve the same aim", for example in a firm (or corporation), but they may place no importance on cohesion or group goals (when they are different from individual goals).
This is not an issue of unions vs. corporations vs. states; it is the fundamental problem with collectivism, which frequently uses coercion as a means to achieve power or theft.