The issue is the intent.
When socialists start doing stuff like this, it is clear what the long term goal is. The long term goal is to take the means of production from those who have it, though whatever politically palpable means necessary.
Sure, they start off doing a voluntary stock buyout program, but what happens when that program inevitably fails? (perhaps because it takes way to long to takeover a company, or merely that the company owners refuse to sell)
Will the socialists come to the conclusion that their socialist policy didn't work and reverse it?
No. What happens when socialism fails is that the socialists conclude that they didn't go far ENOUGH and then they double down on their mistakes.
In this situation, "doubling down" would be increasing the tax, forcing the owners to sell at a given price, and eventually straight up confiscation of the business.
When people in the government start yelling about how they want to take the means of production, even voluntarily, the proper response is to run away as fast as possible, and take your means of production with you, before they make it illegal to do so.