> Wouldn't it be simplest to just legalize the people who are here and at the same time also open up immigrant visas too?

Any form of amnesty encourages the same behavior in the future.

How many and what kind of immigrant visas is an open question. There's definitely a need for more workers in some fields. Healthcare in particular could be well served by importing (even more) doctors from around the world.

What's not up for debate is whether we should be enforcing our immigration laws. If people different laws enforced, then get the laws changed. There's no unfairness to the current laws. And flooding the country with cheap labor hurts the lowest tiers of the populace the most.