Valid point re: axle disconnect. I've been away from YJs long enough to have let that slip my mind
However, if you welded it, it would then mean you'd be spinning your front driveshaft all the time, instead of letting the spider gears absorb the input from the left-front tire by spinning the center stub shaft in reverse. May require a double cardan front shaft to keep the front shaft vibes in 2wd at speed under control, possibly.
And it would leave you with 4wd that was useless except at play.
Personally, if you're hell-bent on locking the front, I'd throw an Aussie or some such lunchbox locker in before I'd weld it, at least it would then be somewhat drivable in 4wd in the real world and away from the off-road playgrounds. The Aussie lockers are cheap as can be.