If your recovery from your 3rd degree tear was pretty good, and you had no major issues with bladder or bowel incontinence, then it surprises me why they seem to be keeping on about it. Please don't let what they are saying make you doubt yourself and your ability to have a successful VB. FWIW my nan had a 4th degree tear (needed to be knocked out for emergency surgery to repair it), but went on to have 2 more vaginal births with no or little tearing.
Good luck with your decision