It's a concern, but any amount dilution is better than infinite dilution (i.e. turning off the lights).
Assuming even a small/moderately sized team, i.e. other people than just the founders are also employed, a good VC will grant new options to employees. The founders get hurt the most. If the VC's want to keep the founders around, then they need to ensure they're properly incentivized as well.
In some cases, you can get the deal done to take care of your people. Then unwind yourself and move on.