If you care about people benefiting from economy growth you want them to own part of it. This is accomplished by them investing instead of consuming.

If something really crazy like progressive capital gain tax is introduced then a lot of people will rather consume instead of taking bets with a lot of risk attached to it and very little upside. This goes for every high tax: if the upside becomes not very tempting you may just as well settle on what you have and stop trying to improve your situation/produce more as huge part of that surplus will be taken away from you anyway.