There are a lot of different pieces required to go to Mars, land, and return. Some of these, like a habitat that humans can live in for the required transit to Mars and back, we have, or at least, we can make with only small modifications to what has been developed (the Space Station). Some of them, like landers and habitats and space suits for use on the Martian surface, we don't have. Every one of these pieces is a potential bottleneck for a human mission.
What you are basically saying is, we should delay Mars exploration with humans until we have all the pieces developed. The Planetary Society is saying, no, let's not delay, let's do a mission we can do now
The longest usage we have gotten out of a space suit on the moon is three eight-hour walks. The report from the Apollo missions was that the suits were trashed by that point (lunar dust is very abrasive)-- they would not have been usable for another use. Mars dust is not as abrasive as lunar dust, but it is much finer. A different problem. Do you want to send humans to Mars if you then have to tell them "oh, by the way, you'll be on the surface for 500 days, but you can only go outside three times. After that we're not sure your suits will still hold pressure, so stay inside."
Of course, we can develop and test suits for Mars. Developing and testing is something we're good at. But there are a hundred pieces that have to be developed and tested, and only so much budget.
So the question is, do we want to delay, until all the parts for landing and habitation and launching back from Mars have been developed and tested? Or do we go now, doing what we can with what we can do?
