Common misconception, thanks to the all-too pervasive influence of the horribly inaccurate King James translation: the word used in Hebrew does not actually mean "kill". It's more akin to "thou shalt not commit murder" or "thou shalt not kill without justification". Of course, there's a whole new can of worms opened up there to debate whether any killing is justified or not. The Bible itself gives a number examples of when killing could be lawful - capital punishment, war etc - and you'll find much more to read in both Jewish and Christian philosophical traditions. A superficial dismissal based on perceived hypocrisy, however, doesn't stand up to even the most cursory examination.
A common misconception is that the commandments given to Moses were to apply to gentiles.
That is not the case as can be seen from the old testament in general and from the Pentateuch in particular.