Well than I think that the person that got killed needs a bit more practice:
Obviously, they were way too close to someone with a fully charged goopgun in hand if a total newb could stick them. Especially if those are players new to online gaming, they shouldn't be too hard to stay at a distance from...
Of course there are exceptions, like meeting someone right around a corner or in a tight corridor with nowhere to go, but every weapon has advantages like that. Like the flak cannon, or meeting someone at long range in an open field with the sniper rifle, or having the higher ground with a rocket launcher, or the link gun lockdown, or being pinned by stinger secondary, etc etc etc...