Why?
They aren't using debt to fund the buybacks. I don't see an issue with it.
If you look at an individual company you are probably right. If you look at the entire economy there is an issue. (micro v. macro economics)
So from a macro point of view, why is it a problem?
After the Great Recession, the Federal Reserve lowered interest rate target level to 0%-0.25%. This was used to stimulate the economy. Around 2011, most companies were profitable but needed/wanted to make upgrades to their stores. They took out loans to do just that. Around 2016 the Federal Reserve started to raise interest rates. A side effect of this action is that interest rates on the corporate debt goes up. This means there are a lot of companies with debt they cannot handle in a recession.
A recession is likely by the year 2020.
I would prefer that the companies not buyback stock but hold onto it for the next recession.
Sources: https://www.cnbc.com/2018/11/21/theres-a-9-trillion-corporate-debt-bomb-bubbling-in-the-us-economy.html https://www.cnbc.com/2018/09/12/the-biggest-red-flag-for-the-next-recession-corporate-debt-to-cash-ratios-top-economist-says.html https://www.latimes.com/business/la-fi-corporate-debt-risks-20190120-story.html https://en.wikipedia.org/wiki/Federal_funds_rate#/media/File:Quarterly_gross_domestic_product_and_federal_funds_rate.png
The bigger concern for me is the increased strain on the national debt.
The Simpson-Bowles Commission was designed to see what could be done about the national debt after the 2010 midterms due to the rise of the TEA Party.
There are two main ways to tackle the debt: lower spending or raise taxes, preferably doing both at the same time. The democrats don't want to lower spending on social welfare programs and the republicans don't want to lower spending on defense programs. And neither the democrats nor the republicans want to raise taxes due to corporate lobbying.
And to top it off former Joint Chiefs of Staff Chairman Mike Mullen said back in 2010 the national debt was a major concern.
The problem has gotten worse with nobody wanting to implement a solution.
Sources: https://www.politico.com/story/2012/12/mike-mullen-focuses-on-debt-as-security-threat-084648 https://en.wikipedia.org/wiki/National_Commission_on_Fiscal_Responsibility_and_Reform
(post is archived)