It depends on the bar/pub, IME. I haven't drunk in 17 years, but am more than happy to join friends on a night out, and drink whatever interesting-looking soft drinks the pub has available. Only on a handful of occasions has some eejit made an issue of it.

I live in a region where tipping is near zero in bars, so that's not an issue. And as for the owners, well, I'm sure they're happy with the MASSIVE markup on the drinks they serve me.

I spent the years between 1982 and 1998 as a non-drinker. I regularly sat at bars with friends or alone. I started with diet coke but then had trouble sleeping so switched to club soda. Eventually I discovered O'Douls.

I always tipped the bartender (and dancers, if that's the sort of place it was) and never felt unwelcome. It can be quite amusing to watch others make fools of themselves as they reach the saturation point.

This.
The markup on soft drinks is way bigger than booze even if the customers tend not to drink as much.

Percentage-wise, yes, but not in absolute terms. A $2.00 soda probably costs the bar $0.05 in syrup and labor, for a markup of $1.95. A $5.00 tap beer probably costs the bar $1.00 total, for a markup of $4.00. Markup on cocktails is even more - booze is where full-license restaurants make their money. Margins on food tend to be razor-thin, when you figure everything in.

Also, most boozers at a hotel bar will have more than one, whereas the soda drinker will very rarely purchase more than one unit. I always keep that in mind if I'm not drinking. $10 for a club soda and two hours at the bar, keep the change, will ensure that the soda stays full and that the bartender doesn't begrudge you, and is still a hell of a lot less than I'd spend on alcoholic drinks. Each seat at a bar, just like each table in a server's section, represents potential income. 20% of my two-dollar tab isn't much in comparison to 20% of the tab for a guy who downs four martinis and then buys drinks for the ladies on the other side of the bar too.

Can't speak for other countries, but a pint of draught beer in the UK has only a little over half actually going to the bar:

http://ale.gd/blog/wp-content/upload...nfographic.png

At least in our neck of the woods (PDX area), there are nearly as many bartenders who take pride in their "mocktails" as their custom cocktails - and I have found (as someone who will order a non-alcoholic drink about half the time in a bar) that by just asking the bartender to mix up an interesting non-alcoholic mocktail of their choice, you get good results. (I wouldn't try it in a dive bar, of course, but in the type that the OP is describing, it is decently likely to work well.)

I've never felt badly about not tippling in a bar, as long as I'm spending money and not merely loitering. (Economics of the margin being great or not!)

In most places it's nothing to do with tips (why do Americans bang on about tips the whole time?), it's more a matter of social custom, which I think is what the OP was asking. And, in many places, with increasingly stringent drink driving laws, bars are much more used to customers not drinking. But clearly you have to buy enough food or drink to earn your seat for the evening.

Certainly, in the UK, pubs are only surviving because of food nowadays.

Are Non-Drinkers Welcome at Bars?
 

Servers including bartenders are often paid less than a living or minimum wage in the United States. The remainder of their paycheck comes from tips. Tips are often the only mechanism that allows a server to make enough money to survive. This system may be different but it is why we are always banging on about tips.

My solution is to just work more on the road. Get as much done as possible and then not work as much when you're home. That, gym, shopping, etc. That said, no bartender is going to refuse to serve anyone who isn't buying alcohol. Just tip really well if you're in that chair for a long time.