Any friction will ultimately affect "conversions", although I think the friction is probably smaller that we'd think. Most people don't spend much time reading and fretting about the TSA online, so for those, standing in line for half an hour and having your passport stamped is just part of the excitement of travelling (for less experienced travelers). As a fraction of the total time and bother of intercontinental travel, it's almost negligible.
"Most people don't spend much time reading and fretting about the TSA online"
That's only true for countries under the U.S. Visa Waiver, which are maybe 5% of the world's population (basically European Union and Australia).
For the remaining 93% of us, we have to think long and hard and plan far ahead before visiting the U.S., and that means being aware of all the issues or risk deportation.
