We can visit Mars for a short time like we did the moon but the soil is toxic and the radiation is intense. We won't stay very long.
The problem is, it's a 2 year trip, minimum. To the moon is only a few days.
That's a LOOONG time to go without an equipment malfunction that could cost everyone their lives.
And MOST of the mars landings ended in failure
Most people don't have a clue how big Space is.
If the sun was the size of a golf ball the nearest star would be about 760 miles away.
It would take the entire energy output of the world for three years to propel a spacecraft the size of a Shuttle to 20% the speed of light.
...and Mars is relatively "close".