You can leave early and suffer few harmful effects. Out there in the real world most people don't really know what a PhD is and will think you're probably cleverer than they are just for starting one. However what potential employers will know is that you have given up on something that you have started and will worry about what commitment you can offer to them.
Research is not the only career you can go into with a PhD. Sales reps and technical advisors in lab supplies companies usually have PhDs, so do many patent lawyers, teachers, technical writers, publishers, management consultants and members of any other profession that needs specialists.
If you really want to give up then you should talk to your supervisor about changing your registration to an MPhil. By now you should have nearly enough results for an MPhil and after a few experiments to tie up loose ends you could be ready to write up in a couple of months. That way you'll never have to explain to an employer why you left your PhD, just why you decided to move on after the MPhil which you passed with flying colours.