They seem over-confident in their ability to deal with alien creatures, bordering on complacent. As a company rep, Carter Burke's plan (which he'd undoubtedly raised with his superiors) was to go in with a squad of highly trained Colonial marines with an extensive track record of dealing with unpleasant aliens, determine what happened to the colonists and, ideally, retrieve a sample to return to Earth with.
A number of key elements of this plan smack of hubris (or negligence) rather than intentional malfeasance on the part of W-Y.
Carter Burke would never have agreed to go to the colony personally if he felt that his own life was in danger. As a young, thrusting Company exec he's obviously happy to take extreme risks with other people's lives, but not his own.
The marines weren't fully briefed prior to landing. Those that were briefed had only glanced at their packets.
The marines had an incompetent (new) leader.
Carter Burke was expecting to be able to get in and out with a sample of the Xenomorphs that they could bring back to Earth, despite the obvious (to us) risk of contamination of the biosphere.