Softserve (McDonalds) ice cream is made from milk and other things and in McDonalds the cleaning and sanitising of these machines is dubious at best. Still, millions eat it and we have immune systems for a reason...it's not something I'm willing to do though. McDonalds outlets are renowned for being filthy (kitchen areas) and they have terrible food practices...just find some staff willing to speak out and you'll get all the horror stories.
I'm not trying to stop you from eating it, it's a choice you'll make yourself and your choice (whether right or wrong) will be the right one for you. I think there's better options though.