The art dealer Larry Gagosian is to open two new galleries in New York, bringing the total number of Gagosian galleries around the world to 14.

Is the Gagosian empire like the Starbucks of contemporary art? A megalomaniac attempt to corner the art market?

It may seem so, but this chain store of aesthetic delights is one of the best things happening to art right now. Gagosian is a force for good. This wealthy and powerful commercial enterprise acts as a genuine patron of the best in 21st-century art. Gagosian has standards, and they are impressively high. If you want to see the most serious art of today, it's a good bet you will find it in your local Gagosian.

I recently wandered awestruck among the great sculptor Richard Serra's mighty walls of steel at the Guggenheim Museum in Bilbao. It reminded me that there has still not been a big Serra show at Tate Modern. But never fear. British art viewers did get a good chance to experience his art at its most ambitious – thanks to a terrific exhibition at Gagosian in London. The market thus filled a gap in our public galleries. With real taste and belief in art, this dealer champions (and of course sells) the best.

Gagosian's artists are not all mega money spinners either. The Turner prize winner Richard Wright makes elusive, often impermanent interventions. His art has been supported by Gagosian since before he got his Turner. He is at the opposite end of art from one of Gagosian's pop stars like Jeff Koons.

Yet what most impresses me about this gallery network is the support it can give to the very best and bravest art. The great painter Cy Twombly was represented by Gagosian and had shows at various Gagosian galleries right up to his death. The way he could keep making and showing art so effectively was a tribute to the gallery that enabled it all so smoothly.

It's easy to sneer at the mad prices and glib sales talk of the art market, but the art of today would be poorer without Gagosian. He is the one who pushes the best stuff – it does not get better than Serra or Twombly. And who has the first show at both his new Manhattan spaces? The brilliant Urs Fischer.

Walking into a Gagosian gallery almost always makes me optimistic about the future of art. Keep 'em coming, I say.