It's hard right, people more extroverted than myself have proposed, been proposed to in this way and loved it, found it romantic and went on to have very long and happy marriages. In a way that's cute. But it is tacky right? I am not a snob but it's tacky.
And yes, if someone was going to feel pressured into hastily saying yes, just because it is in public, then they should really not be proposed to in that way. And if your that serious in your relationship that you are going to propose, you should know your partner well enough by then to know if that situation is right for them or not.
Myself, it is going to be secluded, romantic and just between the two of us. If it goes to plan, I had plans last time, but I got tipsy and impatient and it just spontaneously happened in bed one night, not very romantic, did not work out in the end.
Each to there own, if that's what people want to do, let them be, but it's not for me. I feel uncomfortable seeing public acts of affection, am I sure I would too feel uncomfortable seeing a public proposal.