either way it's time to move on

Depends on the content of the message.

Polite yes no maybe is what every polite inquiry deserves. ....

It depends on the message. If it is just hi, then ignoring is OK.

If the message is more than that, like Hey wanna have coffee, then I think reply is helpful to let him/her know what's what.

I'm generally depressed and feel pretty undesirable. So getting ignored helps feed my internal mythology. It helps to confirm how I feel about myself. So yeah... Ignore me.

I guess my preference would be a polite "no thank you" or "not interested", but I completely understand if someone chooses not to respond at all. There's a lot of people out there that have really been hurt before in life and may have a lot of "trust" issues, so for them it's safer and less complicated to not respond.

Politeness seems nicer and more appropriate. To show an attraction is not always easy. Why must we be disrespectful and condescending when the person showing attraction is not attractive to the one being approached? It’s almost like some people consider a compliment of attraction is an insult if you aren’t interested.

I prefer they say yes! Anything else sucks just as badly so it really doesn't matter.

Now I am tempted to send you a flirty email and see if I get a reply before you delete it.

The companion to this is when down the line you discover that someone has barred you without letting you know that they have. Sometimes it occurs within memory span but in others it doesn't and then it becomes "why" did someone actually come to my page and accidentally press my barred button?
The saying "keep your friends close but your enemies even closer" has not been around for thousands of years without justification.