I've seen the opposite. If players know their characters are more likely to stay down if they go down, they can become too cautious. They are less likely to take big risks. If they know that going down can be temporary, they are more likely to take risks with big fun actions.

Stimpacs and medpacs were in the WEG d6 version from the word "Go," so there's historic inertia at work as well. In d6, each successive use was harder and harder to heal the patient, with a night's sleep (I think, or maybe a day w/out using one) to rest the check to "easy."

-EF

Well, the idea of stimpacks being a "quick heal with no roll" is fairly new, and medpacs in prior editions were more like compact emergency first aid kits with medical kits being the label for a more extensive/comprehensive collection of medical supplies. And prior to FFG's implementation of stimpacks as a form of "video game style instaheal", using either a medpac or medical kit required some kind of roll in order to benefit from them.

Saga Edition was really the first Star Wars RPG to have an "quick heal with no roll" in the form of a character's Second Wind (works fairly similar to D&D 4e's Second Wing, restoring a quarter of the PC's total hit points once they've lost a certain amount of hit points), though it was generally a "once per day" in Saga Edition (barring the selection of certain feats or talents that added more Second Winds per day).

Memory might be a bit fuzzy on the subject, but I don't recall the issue of stimpacks being that it was a means of allowing a character to quickly reduce their Wound Threshold, but more that having to use an item to do it was the concern, due to the stimpack method feeling more like something you'd see in a video game (pick up/use health item = regain HP) than you'd see in Star Wars.