You're apparently unaware that not all tax appears on your salary receipt. Employers have to pay 20% to SS, on top of the 11% that the employee pays. (This amount doesn't count toward your gross income for IRS purposes though, which is relevant to your point)
The distinction is largely a technicality, all the more because both parts of the SS contribution are paid by the employer directly to the state, but it does have one effect: because the 20% don't show up in the salary receipt, most portuguese people are, like you, blissfully unaware of what the real tax rate on their salaries is.
You're responding to a statement I didn't make. I just corrected the common misconception that the SS tax is 11%, it's not, it's 34.75% [0]
What would happen if those taxes were lowered is for economists to speculate, I'm not one (even then, as the joke goes, put a question to two economists, get three different opinions)
42000€ per year gross salary lands you in the 28.5% income tax.
A yearly gross salary of 42000€ is about +/- 1800€ salary/month.