I often dine alone. If I were "forced" to sit at the bar, I would never patronize that restaurant again. It is one thing to say, "There are no tables open right now - would you like to eat at the bar, or shall I put you down to wait for a table?" If it gets me eating quicker, I'm all for it. However, to say, "It doesn't matter what tables are free - you're single, and you're not taking up one of our precious tables," is extremely rude service.
The bar is for people to drink. While you may get food there in many restaurants, that is a secondary function. If I'm taking up a bar seat and drinking soft drinks with my meal, that also is a loss to the restaurant.