If you do need to have the paperwork available, I think that a music stand is easier to sing with than placing the paper on a table or chair - it allows you to keep your head up more & project better.
Ideally we would all prepare things to perfection before performing - but then its not an ideal world. If you are going to one or two pub sessions per week, with many of the same people present, then I think its better to use a sheet as an aide-memoir than to keep singing the same few songs at every occasion. Definitely the songs should be in a performable state though - its a bit cheap to just read-sing something you're not even familiar with.
Having said that - it is usually the case that the performance will be orders of magnitude better if the sheet can be dispensed with. Things that are good with the music stand can go on to become stunning without. I compromise by doing some with & some without. It tends to work out that there are some transient songs that I sing only a couple of times anyway, but anything that I really take to tends to stick & join the "by heart" repertoire.
I certainly don't think it should be frowned upon - we should judge the performance for what it is, not for whether or not a stand was used.

Kris