This was not an either or.
Haslem was a FA. Beasley was under contract. To sign the South Beach big three to the highest possible $$$ amount, they had to move Beasley.
Haslem, as I mentioned, was a FA. Miami owned his bird rights. After Miami inked James, Wade, and Bosh, the bird rights allowed them to resign Haslem to any $$$ amount above the cap w/o using their mid-level (which went to Miller).
Moving Beasley was a cost of doing business to sign the other big 3. That's all.
Mk