This post has been updated.

Fast growing startups with debatable finances have been effortlessly raising billions of dollars at stratospheric valuations. Big tech companies are sinking cash into risky industries they have no expertise in. And the Nasdaq recently climbed above the 5,000 mark for the first time since 2000.

Are we back in tech bubble territory?

One person who thinks so is Mark Cuban. In a blog post last night the Dallas Mavericks owner, who has credibility on bubbles since he made a fortune selling his startup right at the peak of the last one, says the bubble we are in now is even worse than the tech bubble and bust of 2000/1.

Why? He writes:

Because the only thing worse than a market with collapsing valuations is a market with no valuations and no liquidity. If stock in a company is worth what somebody will pay for it, what is the stock of a company worth when there is no place to sell it ?

Here’s some explanation: Almost everyone (including Cuban) agrees that if there is a tech bubble today, the risk is concentrated in the hands of private market investors, rather than stock market investors, as was the case in 2000. That’s because startups and other privately held companies are waiting much longer to go public now. Financing for pre-IPO tech companies is arguably more plentiful than ever.

Some people think this reduces risk because if a bubble were to burst it would only be venture capital funds, rich people and startup employees (who are paid partially with equity) that would get burned, rather than millions of moms, dads and people trading stocks in their basement for a living, as was the case last time around.

But Cuban actually sees this dynamic as a problem. He argues that there are thousands (225,000 to be precise) of angel investors in the US that have invested significant amounts of money in private startups—and not all of them are necessarily hugely rich people who can swallow their losses. “Like the crazy days of the internet boom, I wonder how many realize what they have gotten into?” he writes. Many ordinary people could be exposed through equity crowdfunding platforms, which require as little as a $5,000 investment, he says.

Cuban has “absolutely” no doubt that most of these investors are underwater (i.e their investments are worth less than what they paid for them). Because the market for small tech IPOs has dried up, they have no way to exit their investments. Which could be a problem”for all those widows and orphans who will put their $5k into the dream only to realize they can’t get any cash back when they need money to fix their car ” he writes.

It is an interesting argument. If he is right, it is not entirely clear how this dynamic would flow back to the stock market, where prominent tech companies such as Apple and Google are arguably undervalued using traditional measures. Let alone the real economy.

In an email to Quartz, Cuban said “that’s not relevant” and further clarified his thesis. ”A bubble is when uninformed investors, in search of a huge payday invest money at prices far greater than their actual value and end up getting a reduced amount in return,” he said. “In this case, with the private market lack of liquidity. Ten minutes after they invest, their investment is basically worthless. That’s a bubble.”

And because it is easier than ever before to be an angel investor, he says the risks could be magnified rather than dispersed among more people. The rise of equity crowdfunding platforms means that today’s private market investors are not necessarily more financially insulated than yesterday’s stockmarket investors who were so badly burned when the last bubble popped. The “accreditation bar” is “very, very low,” he says.

Update 3:37pm ET: After some pushback, Cuban has published a second blog post, defending his view. Among the key quotes:

How many people have been pitched an app that is going to be the next …….. How many people have been pitched to invest in that app ? Has anyone not been pitched investing in an app ?

Cuban goes on to admit that he does not know how many individual investors in the US have invested in small tech startups but says: “My guess is that its as big as the number of…day traders in 2000.”

Read the second post in full here.