I read the first page of responses, but it looked like there were several so I didn’t really read any posts further than that (because I do other things in the day

), but from what I read no one really touched on any reasons other than “It’s gross–I’ll get germs.”
Personally, I do not receive under both Species, and not mainly for any sanitary reasons (although I do have an aversion to sharing a cup with potentially a hundred strangers, this isn’t the main reason I don’t receive the chalice). My main reason is it avoids an occasion for an abuse of the Most Holy Sacrament. The Precious Blood it just too easy to spill when it’s being passed around, sloshed, or, even worse and as I’ve seen, knocked back like a shot. Or when people clumsily drink and slosh it out of the chalice, then wipe their hands (stained with the Sacrament) on their shirt or pants–not the standard recommended way to clean up the spill. Knowing just what is involved in the Sacrament, I want to receive, of course, but I want to avoid any possibility that I would even inadvertently cause a sacrilege or waste of the Sacrament. As much as it appalls me to see others (no doubt inadvertently) abusing the Sacred Species, I can’t allow myself that possibility.
This is to add to the fact that no extra grace is received by receiving both species (my husband quotes St Thomas Aquinas), so there is no spiritual benefit and only the gravest risk of sacrilege associated with receiving under both species. Germs aren’t even the tip of the iceberg. If it is not an express benefit to receive under both species, as our Catholic doctrine says it is not, and only adds up to an abhorrent possibility of profaning Our Lord in the Sacred Species, then it’s best to receive discerningly and with minimal risk, which for me means receiving the Host and making a bow and sign of the Cross when passing the chalice (because while I have received the Host already and so have a bunch of other people and we are all Tabernacles for a time, the Blood is still fully present and deserves the same reverence we give when we genuflect toward the Tabernacle when entering the church at the beginning of Mass).
Now, I know this isn’t the norm among most modern churchgoers, out of respect for the Sacrament I also do not receive in the hand (for much the same reason–it invites too much opportunity for me to drop the Host, to retain crumbs on my fingers and drop them somewhere to be trampled or otherwise profaned–but also because I have not been consecrated for the handling of the Host, while the priest has been set aside out of the whole community for the main purpose of consecrating, distributing, and minding the storage of the Sacred Species) and do not receive from Eucharistic Ministers. My husband and I are unabashed about crossing lines to get to the priest to receive the Eucharist, since it’s his duty to administer it. The most horrific thing I’ve seen in a Mass was a Eucharistic Minister drop a Host on the floor, then kneel and as she was picking it up (which is also the priest’s duty, not anyone else’s), dump the ciborium on the floor as well. That was a tragedy that could absolutely have been avoided, so I am doing my part to avoid that. Out of respect for the Sacrament, we also kneel to receive.
I know this got into kind of a tangent, but I hope you’ll see it as still relevant, since it is all one and the same Person we are receiving, under whichever Species. There didn’t seem to be really anybody who actually refrains from receiving the cup responding, so I thought I would. Basically it’s little or nothing to do with germs or yuckiness factor: it’s all about what is actually going on at the Mass and how I can make sure it’s as holy, reverent, and fulfilling as possible, how I can participate more fully and honor Christ in the Sacrament the most.