Even if people don't find it 'sleazy' per se, you're forcing people who don't want the emails to take two actions to submit the form - one of which requires car

Even if people don't find it 'sleazy' per se, you're forcing people who don't want the emails to take two actions to submit the form - one of which requires care and attention, rather than just hitting the big button. The extra burden alone may well be enough to account for the drop off.