Tipping a bartender or waiter is totally different than giving money to some one for nothing, at least in the US (and I think Canada). I know in a some European countries people don't tip but that's usually because Bartenders and Waiters there get paid a decent wage. In the US Bartenders and Waiters are paid with the assumption they are making a lot of their money on tips, which means their actual wages payed by the establishment are under minimum wage which is allowed by law if you have a job where you make money by getting tipped.
So yes tip your bartender, especially if you expect to be served in a timely manner. If you don't mind piss poor service then by all means don't tip. Personally I tip $2 for the first two or three drinks, usually makes the bartender remember you then $1 a drink after that, $2 if I get a buyback. Being a good tipper means getting a free drinks more often, if I'm a regular I usually get one every 3rd drink at a new bar every 4th, which is pretty good cause most bar owners will tell their staff no buy backs or every 5th or 6th drink.
So yeah if you can't tip don't go to the bar, unless your a regular and you really need a beer, having one bad day at your regular bar means the bartender will understand that your strapped and in a bad mood. But if you can't afford to tip then drinking at home is your best bet as your paying less for beer and you don't have to tip the guy at the corner store.
edit: Typing and helping customers means I got beat too it.