There are a couple parts to answer your question.
First the option is there and it seems to be as safe as anything at this point as long as it is used correctly and with pokefarmer only (using the option in other bots would not be a good option *in my opinion* due to the lack of security precautions VS those in PokeFarmer that are now implemented and will continue to be based on what their findings are). There is nothing to honestly say driving speed will ban you faster, although there are theories and if it becomes *Fact* then bossland and team will remove the option from pokefarmer as it would be counter productive to their own bot, user base and financials.
The second part is that it is highly unlikely that anyone would drive consistently at a speed or in their car for long periods of time to pokestops and catch pokemon on the way.
Pretty much without all of us knowing as much as bossland and team (and they are still getting a handle on everything as well, since these changes are all new) there are some that are going in to a "panic" state and also being cautious by trying to emulate human behavior as much as possible including walking VS driving. Other theories include but are not limited to humanizing the walking on streets vs buildings, water etc..., altitude, setting up and mimicking their own walking patterns or drive patterns during their daily lives. You will start seeing all kinds of future requests to add in to pokefarmer from people that are just paranoid and grasping at straws because they just do not know (like some devs) what is truly happening. This then leads to all kinds of crazy reddit posts, etc... that some take as gospel although it is just a theory.
So to answer your question, it is up to you and the risk your willing to take since no one can honestly 100% tell you that it is worse. My outlook is to make accounts, bot and not being paranoid or worrying. Just enjoy botting. Botting Pokémon Go is definitely cheaper and easier than World of Warcraft!