not being able to use regular pants

this is not really an obstacle if you know how to sew. even less so if all humanity had tails and all pants were designed with that in mind

not being able to sit down comfortably in most chairs

see previous response. also most chairs I've seen have holes in the back anyway

getting too warm in summer

if having one part on our whole body covered in fur was enough to make us overheat we wouldn't have hair on our heads. what's one more? besides, dogs naturally lose their coats in summer. also we're humans, we can shave if we want to.

energy loss from moving it

oh no! I will have to eat an additional 5% more food. whatever shall I do?

not being able to take a clean shit or wipe properly

you do know dogs can lift their tail up to fully expose their butthole right? they do it all the time on dog shows

not being able to lay on your back again

either lie with your tail under you or make it poke out the side. this ain't rocket science. I'm not even sure it would be that uncomfortable

No tails. We evolved past this for a reason.

And that reason was a stupid one fuck evolution give me my tail back. I respect your right to not want a tail but when we get this whole genetic engineering thing figured out I will be first in line