Of course, that is thinking like rational humans. The Klingons would take advantage of that Day 1 Hour 1. Heck, they went and wiped out the Tribble homeworld. The harmless Tribbles! Just imagine if Captain Archer insulted Kang's cousin twice removed... Earth would've been wiped out just to satisfy some honor ritual
Having FTL sensors is vital to keep things in check in Star Trek just to have some viable defense perimeter, IMO.