"arsonist" is a strong word. I don't expect city slickers to understand, but using fire to manage grazing lands is a widely recognized technique:
http://www.sciencedaily.com/releases...0328115430.htm
https://www.business.qld.gov.au/indu...re/when-to-use
https://www.firescience.gov/projects..._FSBrief37.pdf
even on public land used by ranchers:
http://esrd.alberta.ca/lands-forests...ewardship.aspx
I could understand a fine or even the original sentence imposed by the court, but a five year mandatory sentence without the possibility of parole (federal time) is way over the top. Looking at the back story on the case, it really looks like the DoJ wanted to make an example of these men.