Their removal, they intuitively divined, was proposed not to do their race a benefit, but rather to do a service to the owners of slaves.

These objects of the society's pseudo-philanthropy had the sagacity to perceive that, practically, their expatriation tended to strengthen the chains of their brethren then in slavery; for if the South could get rid of its free colored population, its slave property would thereby acquire additional security, and, of consequence, increased market value.

Like cause, like effect.

If the operation of the colonization scheme was decidedly in the interest of the masters, it was the part of wisdom to conclude as the free colored people did actually conclude that the underlying motive, the hidden purpose of the society was also in the interest of the masters.
Garrison did not reach his conclusions as to the pro-slavery character and tendency of the society abruptly.

The scales fell away gradually from his eyes.